In Assassin's Creed Valhalla, Eivor's adoptive brother and clan leader is named Sigurd.
Sigurd Styrbjornsson is the son of Styrbjorn, the Norse jarl who rules Eivor's clan before its migration to England. After political pressure and conflict in Norway, Sigurd leads the clan toward England, where the settlement of Ravensthorpe is established.
Sigurd's discoveries shape much of the game's main narrative. During his travels, he encounters the Hidden Ones Basim Ibn Ishaq and Hytham, whose presence draws Eivor into conflicts involving the Order of the Ancients and ancient Isu mysteries.
Sigurd is not Eivor's biological sibling; the game describes him as an adoptive brother. Basim is also not Sigurd's brother, although he becomes one of the story's most important companions and rivals. Sigurd's relationship with Eivor changes significantly as the campaign progresses.