Björn is a twelve-year-old boy who lives on a small farm in a village outside Kattegat with his father Ragnar, his mother Lagertha, and his eleven-year-old sister Gyda.
When Ragnar returns home from raiding in the Eastern Balts, Björn is ecstatic and rushes to give him a hug. The family celebrates his safe return home. Ragnar informs the family that he will take Björn to Kattegat to attend the Thing so that he can receive his arm ring, which will mark him as a man in Viking society. Lagertha tries to convince Ragnar that Björn is still too young, but Ragnar insists. Björn is happy with this outcome as he has yearned to be a warrior like his father, and is desperate for recognition and to fight in the raids alongside Ragnar.
On the way to Kattegat, Ragnar explains to his son what will happen. They will witness justice through the system led by their chieftain, Earl Haraldson, and then the earl will decide where the clan will raid for the summer. Björn can tell his father wants to choose a different place to raid than the earl. When he mentions this, Ragnar replies, "Odin gave his eye to acquire knowledge. but I would give far more." While camped out in the woods, Ragnar asks Björn what a man does, Björn replies that a man fights and protects his family. Ragnar also tells him the story of how he earned Lagertha's hand in marriage.
Upon arriving in Kattegat, Rollo meets Ragnar and Björn. Rollo congratulates Björn on his growth and in becoming a man. They head to a tavern where Ragnar reveals a device to his brother which would keep a journey west, over open ocean, on a true course.
Björn, Ragnar, and Rollo gather with the other villagers in the Great Hall to witness Earl Haraldson pass judgement on criminal matters. Björn is informed by Ragnar that he must participate in the sentence of the thief by throwing something at him, and then again when Ragnar tells him that he must watch Eric Trygvasson’s death. That night, Björn and another young boy, Olaf Igolfsson, receive their arm rings by swearing fealty to Earl Haraldson. At twelve, Björn is now considered a man. Both boys receive a kiss from Haraldson’s wife, Siggy. During the feast, Rollo tells Björn and Ragnar that Earl Haraldson is known for wanting Trygvasson’s land, hinting that that was the reason for why he sentenced Eric to death. Björn appears a bit shocked and turned off by the casual violence he is forced to participate in, from sentencing a man he doesn’t know to death to throwing things at a man for stealing.
After his first visit to the Seer, Ragnar takes Björn to meet Floki. Floki tells Björn that he has his father’s eyes, and this means he will surpass him in life. Floki explains to Björn that he knows how to talk to trees and thus can make Ragnar the perfect boat to carry him west. Upon arriving back home, Ragnar and Lagertha immediately go to have sex, leaving Björn waiting outside. Rollo arrives and asks Björn where his parents are. He casually says they are having sex.
Though obedient to his parents, Björn resented being put under the supervision of the young Northumbrian monk Athelstan who was captured as a slave from Lindisfarne.
Brought along by Ragnar on his trip to Gotaland for King Horik, Björn was witness to the beginning of his father's relationship with Aslaug. Disgusted, Björn confronted his father about his infidelity, making him swear that it will never happen again. While Ragnar did promise this and tried to keep it, Aslaug had already become pregnant with a son.
Upon their return to Kattegat, Björn told Lagertha of Aslaug and his father's infidelity, though he did not say much out of loyalty to Ragnar. When Lagertha decided to leave Ragnar, Björn was torn. Though he initially decided to stay with Ragnar, through Torstein's urging, Björn eventually decided to go with his mother. Ragnar let them, telling Björn to look after his mother.
Even years after their departure, Ragnar continued to think of them. When he met with the Seer, the oracle told him that he had foreseen that his sons would become famous, possibly even more than him. His son, the Seer said, would marry the daughter of a king, or would sail across a sea without tides. Ragnar asked about Björn, whether he still lived, and whether he would ever see him again. The Seer told him that it was Björn about whom he had prophesied.
Meanwhile, under the thumb of his oppressive new stepfather, the 18-year-old Björn hoped to live alone in the mountains to test his strength and skills. His stepfather, Lagertha's new husband Earl Sigvard, who often sought to shame and humiliate him in front of his subjects, refused. Around this time, Björn discovered that Sigvard had been hitting Lagertha, much to his anger. Björn told his mother that if Sigvard continued to hurt her, Björn would kill him.
When Björn heard of the capture of Kattegat by Jarl Borg, he tried to get Lagertha to persuade Sigvard to assist Ragnar. Sigvard refused, spitefully, but Lagertha marshals a force anyway and rides to assist Ragnar. Locating Ragnar, Lagertha and Björn are a welcome sight. Ragnar particularly marvels at how tall and powerful Björn has grown. Rollo also mentions that Bjorn still can't grow a beard.
After his performance in battle against the West Saxons, Björn is given the epithet 'Ironside' by Ragnar.
On his return to Kattegat from England, Björn formed a relationship with a former slave-girl, Þórunn, who was freed by Aslaug because she realized Björn loved her.
Björn was surprised when Þórunn told him that she was pregnant. After the battle of Mercia, he asked Þórunn to marry him and she said yes. He looked after her when her face was badly scarred in battle. Later, she gave birth to their child: a daughter they named Siggy. Björn sleeps with Torvi, Erlendur's wife, when Þorunn rejects his attempts to have sex with her and tells him to find someone else to be with, due to her feeling self conscious about her nasty scar. Bjorn strikes up a conversation with Torvi, who looks quite smitten by Bjorn and gives her a drink and asking that her husband is coming to Paris when Torvi says she is coming as well, Bjorn notes that she has courage. Bjorn later leaves the party and sits out on the beach depressed when Torvi goes to join him. Although he initially refused, right before he has sex with Torvi, he tells her that he loves his wife right before they have passionate sex on the beach. He later finds Torvi and apologizes for taking advantage of her, and hands her a bracelet as a gift. She tells him that she's neither with child or a child herself, and apologizes too for taking advantage of him. It also becomes apparent that Torvi and Bjorn are starting to fall in love with each other, much to Erlendur's fury.
Ragnar finds Björn unconscious towards the end of the Vikings' failed attempt to get into the city of Paris, with two crossbow bolts stuck in his back. Björn wakes later that night, and while still hurt, he tells his father that he should have never called him "Ironside," doubtful that the gods are protecting him. His father rebuts and questions, "You're alive, aren't you?" to which Björn says nothing. Later, while still healing, Björn is up and walking but holds his arm obviously still in pain. Ragnar trusts only Björn with something secret, which later is shown to be that Ragnar is still alive as when he exits Paris, Björn catches and holds him. He later defends himself and tells his mother, Rollo and Floki he only did what his father asked of him.
After returning to Kattegat with the rest of the raiding party he takes the treasure from the raid and shows it to his family and Queen Aslaug; his younger half-brother Ubbe shows interest in a map of Europe that Björn had taken, believing it to be more valuable than gold. He then publicly denounces Floki as a murderer and has him arrested. Ragnar disapproves of this decision, remarking that Björn is still acting impulsive. Aslaug brings Bjorn's young daughter, Siggy, to him, but he barely acknowledges her. Later he leaves for the wilderness, in order to prove to himself and his father that he can survive on his own.
Björn manages to make the trek through the snowy mountains until he finds an abandoned cabin, where he takes shelter. He sustains himself mainly by setting traps and ice-fishing. A bear repeatedly escapes his traps, and Björn decides to track it down. He eventually encounters it and manages to kill it with an ax and dagger. Despite his speed and agility, Björn is slashed across the upper chest by the bear's claws. He cauterizes the injury to prevent infection. In tribute to his achievement, Björn tattoos his arms and makes a cloak from the bear's hide.
When Kalf and Erlendur learn that Björn is isolated in the mountains, they dispatch a Berserker to assassinate him. Although superficially wounded in the encounter, Björn outwits and subdues his opponent by whipping a handful of fishing leaders bearing heavy fish hooks into his face. He tortures his captive, asking who sent him, but the man refuses to talk, so Björn disembowels him. Björn then goes to visit his mother in Hedeby. Kalf and Erlendur are visibly disappointed that their assassin failed. Björn claims he came to take Torvi away with him, and does so, though Erlendur forces her to leave her son behind. When Björn returns to Kattegat, he is suspicious of the newcomer King Harald "Finehair."
Conversing with his father as they prepare for the second raid on Paris, Björn is rebuked for ignoring his daughter and for separating Torvi from her child. Björn retorts that Ragnar tried to separate him from his mother as a child, but Ragnar replies that Lagertha left him and Björn chose to go with her, though he acknowledges that he had been a bad husband and that Björn should not repeat his mistakes. When Björn is looking over his map of Europe later, Torvi comes to visit him and notices a ring that he had taken from the Berserker. As they start to make love, Torvi remarks that the ring was passed to Erlendur from his father King Horik, revealing to Björn that Erlendur ordered the assassination attempt.
Later, as the Vikings are settling into France in order to come up with a plan for their battle strategy, Björn approaches Erlendur asking about the ring and whether he knows about it. Erlendur replies that he knows nothing of the ring which is relayed in turn to Torvi who says he is lying for she knows it is his father King Horik's ring. When the Vikings travel upriver towards Paris, led by Rollo, the ships are shot at from the forts by Frankish soldiers. When the Franks lower the chain between the two forts, several ships are capsized and sunk. Björn helps many warriors out of the water, including Harald. When returning to their camp, to find it had been attacked, Björn reunites with Torvi and his brothers. After everyone is recovering, Björn tells Torvi that it was all Ragnar's fault. Björn helps Ragnar execute his plan to take the boats across the mountains.
As the days bleed into each other, the Vikings haul their ships across the mountain top. Björn and Torvi are closer then ever. When Lagertha loses her baby, both Björn and Ragnar comfort her. One night as he and Torvi are laying in their bed in the Viking camp Björn confesses his love for Torvi after making love, but unbeknownst to Björn, Torvi sees Erlendur hidden in the dark, aiming his crossbow at Björn. Torvi then changes sides with Björn, putting her body in front of Björn. The next day, Erlendur tries to force Torvi to assassinate Björn, promising to kill Guthrum if she doesn't obey him but Torvi kills Erlendur instead. Bjorn particiaptes in the second battle against the Franks with Bjorn slaying several Franks but the Vikings are eventually overwhelmed with Lagetha, Halfdan and Floki seriously injured and the Vikings are forced to retreat, Bjorn grabs his mother and jumps onto a retreating boat and a bloodied Bjorn is last seen resting in the ship.
Ten years later, Ragnar has disappeared, Björn has married Torvi and had a family with her. Torvi has given birth to one son and one daughter, Hali and Asa. Bjorn has also become a father figure for Torvi's eldest son Guthrum. Bjorn is informed from another Viking that the Wessex settlement was destroyed as soon as they had left Wessex, Ragnar had never told anyone except Floki and kept it a secret. Bjorn relays this nformation to his now grown up half brothers: Ubbe, Hvitserk, Sigard and Ivar. When Sigard says that Ragnar should have told the people Bjorn says that maybe if he had told them they might have killed him. Hvitserk and Sigard are angry at Ragnar for abandoning them when they were kids but Ivar defends Ragnar saying that he choose to invade Paris and become famous rather than avenge a few average viking farmers. Bjorn says that the combination of the Viking defeat and Rollo's betrayal finally broke Ragnar. People talked about Ragnar like he was a god but he wasn't a god he was a man, a man with many dreams and failings. Despite Ragnar abandoning them he is still the greatest man in the world to him. Ragnar returns to Kattegat after a long absence and offers Bjorn and his brothers to go to England with him but Bjorn declines saying he want's to explore the Mediteranean instead. Once Floki's ships are ready Bjorn travels to Frankia where they try to bargain with his uncle Rollo, who is the Duke Normandy to let them past his coastline so they can travel to the Mediterranean without any trouble. Bjorn is introduced to his cousins William, Marcellus, and Celsa. However they are imprisoned, But Rollo agrees to let them through as long as he accompanies them. They reluctantly let Rollo come due to his betrayal years earlier but not before knee hauling him for his betrayal.
Hvitserk, Bjorn, Harald, Halfdan, Floki, and Rollo then sail down the Mediterranean and arrive at a town which would be later known as Spain and slaughter any resistance and steal any treasure they could get their hands on. While staring out at the ocean on a cliff Odin himself approaches Hvitserk and Bjorn and tells them their father is dead. Hvitserk and Bjorn return to Kattegat, but not before dropping Rollo back at Frankia. Ubbe and Ivar try to kill Lagatha again but are stopped by Bjorn, who says they will have to kill as well as Lagatha, Ivar suggests that maybe they should, Ubbe tells him angrily to shut up. Ubbe tells Bjorn that Lagatha killed his mother, Bjorn says he knows and that he knows that he wants revenge and he would want the same thing if he was in same circumstances. He takes Astrid as a lover as revenge against his mother for having taken the power to Kattegat. Bjorn forms the Great Heathen Army with his brothers to avenge Ragnar, before leaving he says goodbye to his mother Lagatha and Astrid and Torvi and tells them both to look after his mother. He avenges his father by easily defeating the forces of Northumbria and killing King Alle with a blood eagle ceremony.The Great Heathen Army then faces the force of Wessex, confusing and outmaneuvering the forces and causing them to retreat. They capture King Ecbert and High Pope. Ivar demands a blood eagle for King Ecbert but Ubbe and his brother convince Ivar otherwise. Ecbert, unbeknownst to Björn, had passed his kingship onto his son, Æthelwulf. Still pretending to be king, Ecbert granted Björn farming lands, telling him since he was king of kings he could do so. He tricked Björn since the real king was his son and is the only one who can grant land. Ecbert committed suicide in his bath. At the end of Season Four, he wants to keep exploring the Mediterranean Sea and Halfdan volunteered to go with him. Bjorn then witnesses Ivar kill Sigurd by throwing an axe into his stomach and is horrified when Sigurd dies.
Bjorn, Halfdan, Sinric, and Bjorn's followers are sailing back to the Mediterranean. Bjorn tells the group that he wants to go to Rome, but Sinric tells him that the Roman Empire is no longer in existence. Bjorn then asks where they should go. Sinric replies that the group should go to an island called Sicily. Sinric informs Bjorn that it would be better if their fleet of ships were seen as traders rather than raiders, that he should send most of his fleet home, and proceed with only three ships. When Bjorn tells Sinric that if does this he would feel naked. Sinric replies, “It’s better to be naked than to be dead.”
Upon arrival in Sicily Bjorn, Halfdan, and Sinric are introduced to Commander Euphemius. They tell him that they are traders, but Euphemius attacks them. Bjorn manages to disarm Euphemius and points his own blade at him. Euphemius then welcomes them to his city. Euphemius informs Bjorn that they aren’t the first Northmen to come to Sicily and that he learned Old Norse from the Kievian Vikings. He then tells Bjorn that he wants him and his men to be his bodyguards. Bjorn agrees. Later, Sinric discovers that Euphemius is merely a client king to the Emir of Ifriqiya, Ziyadat Allah. Bjorn asks to visit him. Euphemius refuses but is persuaded to agree by Kassia, a famous nun, when she threatens to leave him if he doesn’t take the Vikings to Emir Ziyadat Allah. Halfdan wonders who Kassia is since she holds so much power over Euphemius. The group sets sail for Kairouan, Tunisia in Africa.
Bjorn and his group travel by camel caravan across the desert to meet Emir Ziyadat Allah. The Emir welcomes him and offers to trade. Euphemius disappears. Bjorn and Halfdan are given women to pleasure them. Bjorn finds his satisfactory while Halfdan seems disappointed because his wasn’t actually a woman. Bjorn asks if that was a problem for him, but Halfdan changes the subject.
Later at a banquet, the Emir explains that Commander Euphemius had defected to support the emperor of Rome, but he has been captured and executed. The Vikings realize that Euphemius is the meal they are eating and that Kassia is more powerful than she seems. Sinric says that they should leave Africa and return to their ships because Kassia is the one behind everything that has happened, and she is dangerous. Before they can escape, they are arrested and are about to be executed on Kassia’s orders when a sandstorm suddenly approaches. They manage to escape during the sandstorm and sail back to Kattegat.
Bjorn and Halfdan return to Kattegat, he meets his new ally King Svase of the Sami. Bjorn and Torvi end their marriage, but Bjorn promises Torvi that he will always look after her and Erik, Refil, Hail and Asa. He then proposes to marry Snæfrid. Bjorn and his allies discuss how to respond to Ivar's attack, Bjorn assumes that Ivar will attack from the land, and his allies agree with him assuming, that Ivar will not attack the town from the sea. The armies of Lagertha, Bjorn and Ubbe, and of Harald, Ivar and Hvitserk, meet above Kattegat. Lagertha proposes peace talks, but Harald, then Ivar, reject a settlement. Before battle, Ivar takes Astrid and a third of their army towards shore, to protect their fleet. Hvitserk and his group try to flank, but are ambushed in the forest by the Sami. Battle begins, and Bjorn and Lagertha gain the upper hand, as Harald's forces are outflanked.
After the battle Bjorn seeks peace with Ivar and Harald, but is rejected as Ivar says he has to avenge his mothers death by killing Lagetha; Ivar moves to have him killed but is stopped by Harald. The army of Lagertha faces those of Ivar and Harald for a second time but this time with the help of Frankish warriors supplied by Rollo. Bjorn's traitorous Uncle. As Ivar orders the Frankish reserves onto the field, Lagertha and Bjorn retreat. As Bjorn prepares to leave Kattegat, he finds Lagertha broken with her hair turned white.
After fleeing Kattegat in a hurry Bjorn, Ubbe, Lagetha, Torvi and their children flee to the same hut he had sought shelter in decades earlier. Rollo finds them and urges Lagertha and Bjorn to return with him to Frankia, revealing himself as Bjorn's possible father. Bjorn rejects both Rollo's offer and Rollo as his father. Bjorn tries to kill Rollo but is stopped by Ubbe and Lagetha. Ivar finds the hut, but Lagertha and her followers have already left, leaving a crazed Margrethe behind. They steal a boat and sail for England. At Heahmund's suggestion, Lagertha, Bjorn and Ubbe are to be allowed to settle in East Anglia in return for fighting against other viking incursions. Bjorn has a brief fling with Princess Elsewith of Northumbria and possibly impregnated her with his child.
Bjorn is approached by and bonds with Magnus, who seeks vengeance against Alfred. Magnus suggests to Bjorn, Ubbe and Lagertha that they should join Harald. Ubbe and Lagertha do not believe Magnus' claim about being Ragnar's son. Bjorn fights with the English against the forces of King Harald along with Ubbe, Lagetha and Torvi and they drive back Harald's forces. Bjorn is cut across the eyes in the battle leaving a scar and takes Gunnhild, Earl Olavsonn's wife, who was killed in battle captive, in the chaos Lagertha vanishes. Bjorn ask Gunnhild about His Mother's Whereabouts, but she cannot help him and in turn makes her into a free woman and she hits him to test her freedom. Meanwhile and Alfred grants the Norsemen the Kingdom of East Anglia; Bjorn and Gunnhild could not enter the church due to their beliefs and go to a cabin, where she consorts him and they kiss passionately, unhappy about Ubbe and Torvi's conversion to Christianity. Bjorn realizes he doesn't belong in England and wants to take Kattegat back from Ivar and decides to make an alliance with King Harald. Bjorn bids farwell to Ubbe and Torvi, aplogising for to Torvi for abandoning her and grateful he has four beutiful children with her. In York Bjorn is welcomed by Harald and Magnus, but when Harald realizes Bjorn and Gunnhild are in a relationship he is unhappy.
In York, Harald makes the same deal with Bjorn that he had with Ivar: when Bjorn dies, Kattegat will be Harald's. Bjorn tells Gunnhild that he thinks he has never been in love (Despite the fact that he has professed his love to both Thorunn and Torvi) and he is afraid to ask her if she loves him, Gunnhild tells him that she respects him more for saying that and that she keeps his words in his heart, Bjorn tells her that he loves her and they go to bed. Bjorn then marries Gunnhild, much to Harald's jealousy. Bjorn, King Harald and their army sail through a storm to reach Norway. Harald is frustrated by Bjorn's behaviour and a deadly confrontation breaks out between the two which is soon prevented by Gunnhild. The two shake it off and bump wrists. While marching toward Kattegat with King Olaf and his army, Bjorn is reunited with Hvitserk and they align to take back Kattegat from Ivar. The combined armies attack the walls of Kattegat from two directions. However, the defences are too strong and they are forced back. Bjorn appeals to the citizens of Kattegat and says that Ivar is their enemy. Ivar fires an arrow at Bjorn to silence and kill him but Bjorn stops the arrow with a shield before walking off to join the others who retreated. Bjorn tells Gunnhild that he thinks about Kattegat, about Ragnar and his mistakes as a father, that she is an extraordinary woman, Gunnhild reveals that she wants to have a child and they have sex passionately and romantically. Ivar's wife Freydis sneaks out to the attackers' camp. She exposes Ivar's murder of Baldur and Thora and the hidden door to Bjorn, Hvitserk, Harald and Olaf. A second assault begins in the morning Bjorn shouts to the people of Kattegat that he does not want to kill them, only Ivar telling his warriors to stop fighting to stop the bloodshed. Most of the defenders give little to no resistance, leaving Ivar's housecarls outnumbered and defeated. Harald is seriously wounded while saving Bjorn's life during the skirmish with the housecarls but they cut down Ivar's housecarls and are victorious. When Bjorn and Hvitserk enter the hall, Ivar has vanished. Bjorn is declared King by Olaf where Bjorn is reunited soon after with his believed to be dead mother Lagertha much to Bjorn's joy and his brother Ubbe, who was seriously injured in a battle with the Danes. Lagertha gives Bjorn the sword of Kings hailing him King Bjorn, King of Kattegat. Bjorn had a vision of his father about power and the Seer who tells him that the war is not over.
Bjorn is first seen adjusting to his new life as King of Kattegat. Gunnhild reveals she is pregnant with their child. He punishes the prisoners from his previous war with Ivar, by banishing them from Kattegat. He then establishes a project that will make Kattegat one of the wealthiest cities in Scandinavia by establishing trade agreements with several Norse countries. He would later be informed that King Harald survived his wounds during the Siege of Kattegat and now remains a prisoner in his own kingdom by King Olaf. Bjorn assembles a strike force to rescue Harald, but he loses many men in the ensuing struggle because of a trap that Olaf had set in the water, and is forced to retreat. Olaf soon reveals that he will hold an election of who will be the first King of Norway. Various Norwegian earls, princes, and kings were assembled to attend the election. At the beginning of the election, things were going well in Bjorn's favor, but then suddenly, many other nobles begin to elect King Harald instead, much to the chagrin of Bjorn. Harald eventually won the election and became Norway's first king. Kjetill Flatnose soon revealed to Bjorn that Harald had meant to kill him. Bjorn barely escaped. He arrived back to his kingdom only to witness Lagertha's funeral, who's death he sensed during the journey. After giving a heartfelt eulogy, Bjorn vowed to avenge his mother's death.
He discovered that his younger brother Hvitserk murdered Lagertha and ordered him to be arrested. Hvitserk was then brought into Bjorn's court to answer for his crimes. Bjorn in a fit of rage, beaten Hvitserk and then sent him away to be chained up. Bjorn then eventually ordered Hvitserk to be burned at the stake. During the execution, Hvitserk began to accept his fate gladly. In disapproval, Bjorn then gave Ubbe permission to save his brother's life. Bjorn then exiled Hvitserk in a fit of rage. He then informed his people that King Harald will most likely send his army to attack Kattegat since Bjorn is posed as a threat to him and his complete dominion of the whole country. His wife Gunnhild then rallies the people of Kattegat to make a stand with Bjorn against King Harald.
Bjorn begins an affair with Gunnhild's slave, Ingrid. When Gunnhild discovers them together, she makes the suggestion that Bjorn take Ingrid as a second wife, and Bjorn hesitantly goes along with her plan. It's a unique solution to a problem Bjorn has always had with his women. Once he's "made his conquest" he tires quickly and moves on to another woman. After the wedding ceremony and feast, Gunnhild puts on a brave face, telling Bjorn to go to Ingrid. He lingers, obviously feeling guilty over the pain he's caused her. But she insists. He made a decision and now he needs to follow through with it. Bjorn's essentially failed as a leader at this point because his decision-making skills have all but disappeared after finding out that his decision to make Ivar's bodyguards, led by White Hair, outlaws instead of killing them led to Lagertha's death. Gunnhild is starting to realize that Bjorn has changed for the worse. Letting Ingrid into her life was the only way to ensure that Bjorn would be a father to his child. The way Bjorn kisses Gunnhild's stomach before leaving to consummate his marriage with Ingrid is quite heartless. He showed zero emotion towards her, it was all about the child and Ingrid.
Bjorn sent his captain and friend, Erik the Red to scout for any of King Harald's forces who are preparing to attack. Instead, Erik finds a group of foreigners and after an intense fight, goes back to Kattegat with the remainder of his forces to report this foreign enemy to Bjorn. It did not take long for Bjorn to realize that this new foreign enemy is the Rus led by Prince Oleg, and they intend to invade all of Scandinavia.
Bjorn then sent Erik on another mission to inform King Harald of this great threat. Harald then imprisoned Erik, since Erik was banished from Harald's kingdom years before. Either way, Harald intended to execute Erik then changed his mind and began to call Erik into his court. Erik revealed to Harald that the Rus are coming and are planning to invade. Harald then sends Erik to Kattegat under the condition that Bjorn sends himself and his forces to Harald's aid. Bjorn eventually accepts Harald's proposal and comes to prepare for the coming invasion. King Harald summoned all his vassals to come to the aid of the defence against this invasion. Only a few of Harald's vassals answered the call. Bjorn was concerned about this and then sent Erik on another mission to call more nobles to aid in the defence in his own name instead of Harald's. Despite these efforts, it was eventually becoming clear to Bjorn that no one will come. Bjorn and Harald finished preparing the defences and were now ready to fight. The Rus eventually came and stormed the beaches. The battle slowly began to turn in the Rus' favour due to them heavily outnumbering the Vikings. Harald fought valiantly but was soon overwhelmed and heavily wounded by the Rus soldiers. Despite a fierce resistance the Vikings were eventually defeated and were forced to retreat, Bjorn stayed on to fight on with a small contingent of Norse Viking Warriors until he was stabbed by Ivar himself in the ensuing fight. Bjorn has survived the injury but is fatally wounded.
A dying Bjorn is brought back to Kattegat by his warriors and wives. His anguished breathing and the truly ugly and infected sword wound from Ivar makes it clear he has little time left. When Gunnhild informs him that the Rus are outside the gates, he asks her to help him with his armor one more time.
Bjorn rides out to face the invading Rus army on his own, barely staying on his white horse. The Rus are shocked and confused, having been told he was dead. Even Ivar looks spooked. Many believe him to be a ghost or to truly be a god. Ganbaatar says that Bjorn is not a ghost, and that he will prove it. He rides out towards Bjorn, and shoots three long arrows directly into Bjorn's chest. Somehow, Bjorn manages to not fall off his horse, but instead pulls out the arrows and uses the last of his strength to raise his sword, the Sword of Kings, one last time. At his signal, all the Vikings who have answered Bjorn's call for help come over the hills, surrounding the Rus. While he never reached the same level as his father, Bjorn's dying acting of turning into an arrow-ridden symbol ultimately saves his people.
Bjorn is buried in a lavishly decorated tomb. He has been placed sitting on his horse for all eternity. In Gunnhild's eulogy, she names him the "King of all Norway" and the "Man Who Could Not Die."
Bjorn is a great warrior in all respects, just like his father. As a young child he tries to keep his parents from fighting. He also wants to become a man in society so he can go on raids with his father and uncle. Norse society adheres to the belief that a “real man” is a killer, so Bjorn is eager for the chance to fight to prove his manhood. This is evident in how when he’s asked what a man does, his first answer is, “He fights.” Ragnar approves of this response, but nevertheless reminds him that they do more as well. Like all children, Bjorn has his moments of being a bratty kid. This happens especially around Athelstan. Like most of Norse society, Bjorn scorns him for being a Christian and a slave. He is shown to be indifferent and even cruel towards Athelstan. Thankfully, Bjorn grows out of it, and openly laments Athelstan’s death. He thoroughly rebukes King Horik’s cruel words about the priest being a traitor and worthless individual. At times, Bjorn seems to be the reasonable one in his family. Unlike his father, he appears to be much more in-tune with the emotions of those around him, which becomes even more apparent when he grows older. Young Bjorn can go on some very philosophical tangents regarding the gods and fate at times. Rollo occasionally pokes fun at these tendencies.
As an adult, Bjorn is Ragnar’s most trusted lieutenant and right-hand man. He shows extreme loyalty to Ragnar even after years of separation. For example, after the Vikings return from Paris, he rallies the people to Ragnar’s side and reminds them of where all their wealth and success has come from. Bjorn assists his father with his strategies in battle, such as Ragnar’s plan to fake his own death to get inside the walls of Paris. With the death of Ragnar, Bjorn becomes arguably the most renowned Viking in Christendom aside from possibly his mother. With his own people, him merely stepping into Kattegat was enough to shock everyone. The only person who is not frightened of him is Ivar, and even Ivar will later admit to Bishop Heahmund that he is a little scared of Bjorn.
Like most Viking men, Bjorn yearns for glory on the battlefield and a place in Valhalla. He is passionate about fighting and eager to battle. He is a highly skilled warrior, even when he is young. He was strong enough to match Rollo in a drunken brawl and in his first battle is fast enough to get through without ever been struck. The true testament of Bjorn’s prowess as a warrior comes during his time alone in the wilderness in Season 4. He survives for several months in the icy mountains, manages to track down and kill a bear with only a hatchet and knife, and outwits and overpowers a supposedly invincible Berserker who was sent to assassinate him. He calms down a bit after Season 4 though. Except for the Siege of Paris, where nearly everyone had a brush with death. Bjorn continues to prove deserving of his nickname “Ironside” all the way into Season 5, proving hard to wound in any battle.
Bjorn tends to be the most emotionally stable of the brothers. He is noticeably much more mellow and agreeable as an adult than he was as a child. Bjorn has a somewhat different personal code than most other Viking men. He refuses to rape women in raids or slaves. After his time living in the wilderness, Bjorn tends to act cold and distant to most people. While he still is a lot less willing than most Vikings to kill or throw away lives without need, he has definitely hardened since he was a kindly young adult. It’s clear that Bjorn doesn’t have his father’s intelligence or penchant for outside-the-box thinking. When he realizes that Ragnar doesn’t trust him to follow in his footsteps, this prompts Bjorn to strike out on his own and do some traveling to prove his worth to both himself and Ragnar.
Bjorn is a bit vain when it comes to his appearance. He knows women, and men, find him attractive. He takes great pride in his battle scars, bearskin cloak, and tattoos. His tattoos and hairstyle are clearly modelled after the ones Ragnar had in his younger years. He is clearly attracted to women who are assertive and confident. His youth and inexperience with women often show when he is unable to understand his wives’ choices or actions. He becomes more attracted to Thorunn and Torvi as they grow more self-possessed. But his fourth wife, Gunnhild, takes the cake, being almost as tall and muscular as him and not afraid to call him out.
Bjorn’s courage, deep devotion to his parents, and unshakeable code of honor are all similar to the personality of the god Baldr. Baldr is the son of Odin and Frigg. This connection to Baldr is strengthened by the deaths of both Bjorn and Baldr. Baldr was almost invulnerable, except to mistletoe. This flaw is exploited by Loki who makes a mistletoe spear and tricks Baldr’s blind brother Hodr into shooting it and killing Baldr. Bjorn, who’s earned the epithet “Ironside,” is killed by his brother Ivar who like Hodr is disabled.
Bjorn and Ragnar are devoted to each other as father and son. Like his father, Bjorn also lusts for glory and fame and is curious about other cultures. Although they often have disputes due to Bjorn’s impulsive nature. Bjorn can chafe under his father’s rule and lacks the patience necessary to secure victory. Bjorn often does not see Ragnar’s decisions for the long plays that they are. Ragnar becomes upset with Bjorn after he arrests Floki for the murder of Athelstan. Ragnar had planned to confront Floki alone and in confidence, but Bjorn arrested Floki in a public setting. Ragnar had deemed Athelstan’s death as the act of an errant friend and disliked having his hand forced by Bjorn.
- Due to Lagertha originating from the Gesta Danorum instead of the Saga of Ragnar Lodbrok, Bjorn was the son of Ragnar and Aslaug not Ragnar and Lagertha.
- As a young adult in Season 2, Björn's status in Norse society appears to be that of a Drengr, who is a young man of fighting age, particularly from a middle to upper-class background. If he was granted land by his father, an earl, Björn could become a Thegn and be able to lead men into battle.
- As both his father and mother became the respective earls of Kattegatt and Hedeby as of the episode Blood Eagle, Björn could potentially inherit a strong powerbase for his future rise in Norse society.
- As of the Season 2 finale, and with the deposition of King Horik and his family from power, Björn, along with his half-brothers, now hold the status of Budlungr or "prince" in Norse society, now that his father is King of Denmark.
- The saga Tale of Ragnar's Sons states that Björn would come to rule over most of Sweden.
- In Norse society, you were not supposed to say the actual word for bear out of fear of summoning the creature, hence the word "björn" (bear) was used instead and eventually became the widely used word and the old name was forgotten. Likewise, ulf or ulfr, the Norse word for wolf was avoided and the word "vargr" was used instead. "Vargr" means outlaw.
- Ragnar's converted dead entrance in Paris was actually made by Bjorn years after his death in the city of Luna in Italy. A city that Bjorn believed was Rome. A similar tactic of faking death in order to gain entrance to a city via a coffin was used by a subsequent King of Norway, Harald Hardrada. Coincidentally in A Good Treason, Bjorn is shown seeing a map that he got in Paris. Which clearly shows Rome over Italy and Gaul over France. When Ubbe asks him what it is, Bjorn answers it is his future.
- While Bjorn being a leader of the Great Heathen Army is featured in the sagas, historically Bjorn was dead by that time.
|Season one appearances|
|Rites of Passage||Wrath of the Northmen||Dispossessed|
|Trial||Raid||Burial of the Dead|
|A King's Ransom||Sacrifice||All Change|
|Season two appearances|
|Brother's War||Invasion||Treachery||Eye For an Eye||Answers in Blood|
|Unforgiven||Blood Eagle||Boneless||The Choice||The Lord's Prayer|
|Season three appearances|
|Mercenary||The Wanderer||Warrior's Fate||Scarred||The Usurper|
|Born Again||Paris||To the Gates!||Breaking Point||The Dead|
|Season four appearances|
|A Good Treason||Kill the Queen||Mercy||Yol||Promised|
|What Might Have Been||The Profit and the Loss||Portage||Death All 'Round||The Last Ship|
|The Outsider||The Vision||Two Journeys||In the Uncertain Hour Before the Morning||All His Angels|
|Crossings||The Great Army||Revenge||On the Eve||The Reckoning|
|Season five appearances|
|The Departed Part 1||The Departed Part 2||Homeland||The Plan||The Prisoner|
|The Message||Full Moon||The Joke||A Simple Story||Moments of Vision|
|The Revelation||Murder Most Foul||A New God||The Lost Moment||Hell|
|The Buddha||The Most Terrible Thing||Baldur||What Happens in the Cave||Ragnarok|
|Season six appearances|
|New Beginnings||The Prophet||Ghosts, Gods, and Running Dogs||All The Prisoners||The Key|
|Death and the Serpent||The Ice Maiden||Valhalla Can Wait||Resurrection||The Best Laid Plans|
|King of Kings||All Change||The Signal||Lost Souls||All At Sea|
|The Final Straw||The Raft of the Medusa||It's Only Magic||The Lord Giveth||The Last Act|