Yol is the fourth episode of the fourth season of Vikings. It is the thirty-third episode of the series overall. It first aired on March 10, 2016. It was written by creator Michael Hirst and directed by Helen Shaver.
A Norwegian king and Bjorn, who is accompanied by a new partner, will get welcomed to the Great Hall in Kattegat. King Aelle will end up arriving at Wessex for Christmas and will be unimpressed with the development of family relations. Meanwhile, in Paris, Rollo’s future is going to depend on whether he can win over his new bride, as a papal delegation arrives to arrange a divorce.
In Kattegat, the people are celebrating Yol. Having been set free, Floki visits the Seer who tells him that he has waited a long time for his arrival. He is then instructed by Aslaug to teach Ivar the way of the gods. Ragnar grows closer to Yidu and lets her live in his private home in the woods. Ragnar and Yidu discuss how she came to be a slave. She then gives Ragnar some "medicine" from her native lands, which leads to a drugged night of hallucination. In the wilderness Bjorn encounters the Berserker, sent by Kalf and Erlendur, and kills him. He discovers a ring in the Berserker's possession. Bjorn arrives in Hedeby and intends to leave with Erlendur's wife, Torvi. Rollo is served divorce papers, but has learned the French language, leaving Gisla impressed. He then gives her his Viking band to show his allegiance to her. In Wessex, King Aelle confronts his daughter Judith over her transgressions with King Ecbert. Meanwhile during the Yol celebrations in Kattegat, King Harald Finehair arrives and declares that he intends to become King of all Norway. Ragnar then arrives to see Harald sitting in his Great Hall.
- Travis Fimmel as King Ragnar
- Katheryn Winnick as Lagertha
- Clive Standen as Duke Rollo
- Gustaf Skarsgård as Floki
- Alexander Ludwig as Bjorn
- Alyssa Sutherland as Queen Aslaug
- Ben Robson as Earl Kalf
- Lothaire Bluteau as Emperor Charles
- John Kavanagh as The Seer
- Peter Franzén as King Harald
- Linus Roache as King Ecbert
- Amy Bailey as Queen Kwenthrith
- Dianne Doan as Yidu
- Moe Dunford as Prince Aethelwulf
- Maude Hirst as Helga
- Ivan Kaye as King Aelle
- Owen Roe as Count Odo
- Edvin Endre as Erlendur
- Georgia Hirst as Torvi
- Jennie Jacques as Princess Judith
- Seán T. Ó Meallaigh as Prudentius
- Morgane Polanski as Princess Gisla
- Philip O'Sullivan as Bishop Edmund
- Maxim Boshell as Ivar's Axe Boy
- Stephen Rockett as Hvitserk
- Luke Shanahan as Ubbe
- Elijah O'Sullivan as Sigurd
- James Quinn Markey as Ivar
- Niall O'Sioradain as Priest of Uppsala
- Huw Parmenter as Roland
- Nabil Massad as Papal Legate
- Niall Cusack as Abbot Lupus
- Robert Follin as The Berserker
- Jonathan Gunning as Wessex Fool/Magician
- Conor O'Hanlon as Alfred
- Karen Hassan as Therese
- Tom Hopkins as French Archbishop
- Unknown Baby Actor as Guthrum
- Unknown Baby Actor as Aethelred
- Aisling Goodwin as Shield-maiden
- Tom Leavey as Warrior
- Harald Hårfagre, also known as Harald Fairhair, called "Finehair" in the series, is considered the first King of Norway after winning a great naval battle in Hafrsfjord outside of Stavanger, Norway, uniting all the petty kingdoms into one. A great monument is in place there today, called "Swords in Rock," or Sverd i sten. This didn't occur until between 872-900 though, long after the time period depicted in this episode.
- The Chinese "medicine" given to Ragnar is probably betel nut. It does cause reddening of the teeth. As it is prepared in the episode, wrapped in its own leaf, it is a combination called Paan in some southeast Asian cultures. Paan has stimulant and psychoactive qualities which explains Ragnar's hallucinations and bizarre behavior.
- Yidu is introduced as a Chinese woman captured by pirates and sold to the Vikings as a slave. Chinese trade relations during the Tang Dynasty extended west to the Arabian Peninsula, East Africa, and Egypt but it is unlikely that Chinese woman would have somehow been moved as a slave all the way to Paris and beyond.