In Raid, Torstein, with a tip from Rollo, visited Ragnar at Floki's home after he is wounded during Earl Haraldson's attack on his home. There, he met Helga, with whom he shared a mutual physical interest. He is later invited by Floki into bed with them.
With their old ship confiscated by Earl Haraldson, to be given to Earl Bjarni as dowry for his marriage with Thyri, they discussed risking another trip to England with a boat that Floki can build for them again.
When Ragnar Lothbrok succeeded in slaying the old earl Haraldson in combat and becomes the new earl of Kattegat, Torstein is among the first men to give his personal oath of allegiance to Ragnar, becoming a Hirdmann, a personal retainer and bodyguard to the earl.
Torstein is one of Ragnar's most trusted friends and warriors, certainly part of his inner circle, and often seen with Floki and the others. For a time he harbored deep resentment of Rollo for his betrayal of Ragnar and the killing of their comrade, Arne, even to the point of urging Ragnar to kill his brother despite the Law-Giver's decision to the contrary. Torstein takes part in the raid in Wessex but returns with Ragnar to help retake Kattegat after Jarl Borg's invasion and occupation. Along with Ragnar and a small army let by Björn and Lagertha, he fights against Jarl Borg's forces and succeeds in driving Jarl Borg out of Kattegat.
When Rollo leaves for Götaland in an effort to persuade Jarl Borg to reform his alliance with Ragnar and King Horik, Torstein wishes him success, indicating he has forgiven Ragnar's brother for his earlier betrayal. Once Jarl Borg's been lured to Kattegat, Torstein joins Rollo and Floki in seizing and beating Borg, then bringing him before Ragnar, who condemns him to death by blood eagle. Witnessing the bloody execution of Jarl Borg, Torstein, battle-hardened warrior that he is, is nonetheless as shocked as he is amazed by the gruesome spectacle.
In the last episode of Season 2, Torstein is seemingly killed by Floki with poisonous mushrooms in an effort to win the trust of King Horik. The mushrooms, however, only made Torstein appear dead. Later, when Horik attacks Kattegat and enters Ragnar's great hall, the hooded figure Horik initially assumes is Ragnar turns out to be Torstein, alive and well. Torstein then participates briefly in the skirmish that follows, and then is shown exiting the great hall to leave Ragnar alone to deal, for once and for all, with the treacherous King Horik.
The opening of the third season shows Torstein, along with the rest of Kattegat's men, restlessly awaiting the melting of the winter ice that's kept the Northmen off the seas. Two women, Torstein complains, are claiming he's the father of the babies they're carrying.
Once Ragnar and his Northmen arrive in Wessex to claim and settle the farmland promised them by King Ecbert, Torstein is among those agreeing to join Ragnar in fighting to gain the crown of Mercia for Princess Kwenthrith. The axe, Torstein declares, he'll always choose over the plow.
During an attack on King Brihtwulf's forces, Torstein is struck by an arrow in his upper left arm and quickly takes it out by breaking the end. It later turns out the wound got infected, causing a serious fever. Unable to bear the pain anymore, Torstein asks Floki to amputate his arm, saying he never liked his left arm anyway.
When the Viking army advances towards Burgred's forces on at the Battle on the Hill of the Ash, Torstein asks Rollo to bring him with them despite him being severely weakened. Approaching the top of the hill, Björn first scouts ahead unable to see any Mercian forces, but Ragnar is aware of their presence regardless. Torstein volunteers to go first. When he is spotted by Burgred's soldiers, they launch a volley of arrows at Torstein, some of them were blocked by his shield and two struck his leg. When the soldiers approach Torstein, kneeling on the ground, he mutters "Odin, I come to you" before pulling out one of the arrows stuck in his leg, and using it to kill one of the soldiers. The soldiers then kill Torstein. Later, at the camp, Floki sits next to Torstein's corpse, blaming Ragnar for his death. Ragnar reminds him that everyone is fated to die on a certain day and that Torstein chose to come with Ragnar, just like everyone else.
- As an archer in Norse society seen to be using a recurve bow, there may be a possibility that Torstein has Sami heritage. The nomadic Sami were the only people in Scandinavia to make use of the Finnish Juoksa, a type of bow made from a combination of hickory, horn and sinew.
- Torstein's role in Ragnars Hird would be defined as a Skutilsvein, or 'table-man' who was an officer and advisor of the lord and had the privilege to sit at his lord's table during feasts. Indeed, Torstein has been seen to be sitting at Ragnar's feasting table.
- Additionally, Torstein may even hold the office of Forungi, which is simply translated as 'leader' or 'commander' and designates the leader of a Viking expedition or the chief warrior in a Norse Hird.
- Jefferson Hall is also known to have appeared in the minor role of Ser Hugh of the Vale during the first season of the HBO series Game of Thrones.
- Torstein means "Thor's stone" or "Thunder Stone".
|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|