Þorunn is introduced during a dinner party held by Ragnar where she accidentally spills beer on Björn, who tells her not to worry about it. Björn finds the girl again and asks for her name and that she sit with him, though Þorunn keeps telling him that she must finish her work. Björn asks where she sleeps (in the barn with the other slaves and farm animals) and if she has a boyfriend, to which she playfully answers "Of course". Ragnar notices his son awkwardly interacting with the girl; Aslaug tells him that she is pretty enough, at least.
Björn is unfazed and asks Þorunn to join him at his home so that she may sleep in comfort. She hesitates and Björn tells her that he doesn't want it to be an order but a choice. Þorunn undresses and asks Björn if that is what he wants. It's left unclear whether or not the two sleep together.
Though Þorunn is certainly beneath Björn's status, he is infatuated with her; her feelings, however, are a bit less clear. As time progresses, and Ragnar plots out his next English raid, Þorunn seems to return his affections. Björn's mother, Lagertha, notices her son's interest in the slave and asks her son what the nature of their relationship is. Björn replies that she is a servant, but that he loves her.
The two passionately kiss, with Þorunn admitting her love for Björn, before the latter sets off for England. While Björn is away, Þorunn practices her swordsmanship on the beach. Aslaug stumbles upon her and asks what she is doing. Þorunn tells her she is training to become a shield-maiden as she wishes to be like Lagertha. Though Aslaug questions her as to why everyone seems to want to be like Lagertha, Aslaug explains that she understands and releases Þorunn from servitude. She tells Þorunn that she may continue to serve in the house, but only if she chooses to.
She tells Björn that, now that she is free, she is unsure of her feelings for him. Hurt and upset, Björn makes a remark about being able to have any woman he wants, which in turn upsets Þorunn and creates a rift in their relationship.
Björn apologizes and tells her that she is the only one for him, but she brushes him off until he agrees to fight her in the woods. They meet in the woods were they quarrel for some time until she runs off with him chasing after her again apologizing. Their season together ends with them making love in the woods, pledging their love to each other.
After spending time training with Lagertha to be a shield-maiden, Þorunn invites herself to Wessex with Ragnar's army despite Björn's protests and concern for her safety. Björn is worried that she may be with child. She shows herself a very capable warrior, though Björn is clearly distracted, making sure that Þorunn is kept safe. He is still unhappy that she came to Wessex and the two often argue about it. Björn's worries were well grounded, however, when Þorunn reveals that she is pregnant. He asks her to marry him and she accepts.
During another battle, Þorunn is overtaken by a Mercian warrior and severely beaten, leaving her unconscious. She is saved from certain death by Björn, who is able to kill the Mercian and rescue Þorunn. Björn frets over Þorunn, telling his father that she is pregnant. Ragnar becomes extremely angry that his son would allow the woman carrying his child to join them in battle. Ragnar slaps Björn in disgust.
Þorunn wakes up several days later, she is ashamed of her appearance (the Mercian left a large, v-shaped gash on the right side of her face) and refuses all help. Þorunn sinks into a deep depression, which is worsened by the birth of her daughter. She screams in pain that she does not want the child.
A healthy daughter is born, whom Björn names Siggy after his uncle's lover and the savior of two of his half-brothers, but the news does not brighten Þorunn's spirits who falls even deeper into depression. She feels like a failure, unable to be a true warrior like Lagertha. Björn tries to coax her out into public, but she constantly tells him that he cannot be happy with her due to her scarred face. She refuses to have sex with him, as well, claiming that she cannot please him. Björn insists that he is happy, that he loves her and their daughter, but he doesn't know how to help her.
Later, Torvi finds Björn alone and the two begin kissing, although Björn admits to her that he loves his wife. Elsewhere, Þorunn begs Aslaug to care for her child as she simply can not do it. Aslaug refuses, telling Þorunn that she is being selfish and that Björn loves and cares for her. She tells Þorunn to pray to Freya for guidance.
Aslaug's advice falls on deaf ears; however, as Þorunn's decides to leave Kattegat while most of the warriors (including Björn) are away attacking Paris.
- The word for a slave-girl in the Old Norse language was ambátt. Those who specifically served their masters as concubines were called frilla or friðla.
- Thorunn, as a slave in Norse society, may be of either Baltic, Finnish or Slavic origin. However, since she has a Norse name, she could have been captured in wars among Norse tribes or born in captivity.
- The "Þ" (thorn) in Þorunn's name, though it looks like a modern "p", is pronounced in English as a "th" sound.
- The female name Þorunn means "Thor's wave" or, literally, "Thunder wave".
- Since Season 3, Thorunn's fate is unknown and it is unknown if she will return in Season 6.
|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|