In the Völsung cycle, Sigi is the ancestor of the Völsung lineage. In the Völsunga saga, he is said to be one of the sons of Odin. He is also listed among Odin's sons in the Nafnaþulur. He has a son called Rerir, whose son was Völsung, sire of Signy and Sigmund, who, together with his sister begot Sinfjötli. Sigmund also fathered Sigurd, possibly with Hjordis
He was outlawed for murdering a slave who had outdone him in hunting. With the help of Odin, Sigi fled from the land and led successful raids, so much so that he became king of Húnaland, a country name referring both to the territories of the Franks, also known as the Hugones or Hugas, and the territories of the Huns. In his old age, he was killed by his wife's brothers who seized his kingdom. His son Rerir avenged him.