Sigurd fell in love with Kriemhild, and to gain her hand in marriage, agreed to help Gunter win the hand of Brunhilde, the amazonian queen of Iceland. Having done so, Sigurd and Kreimhild married.
Brunhilde, learning of Sigurd's artifice, orders her husband to kill him, but Sigurd, who has bathed in the blood of the dragon Fafnir, is invulnerable. The task falls to Gunter's "grim retainer" Hagen. Hagen tricks Kriemhild into revealing the vulnerable spot between Sigurd's shoulders, then betrays and murders Sigurd while hunting.
Heartbroken, Kriemhild gives in to her fury and vows to avenge Sigurd's death. She agrees to marry Atilla the Hun and travels to his court. Later, she invites her brothers to feast with them. When they arrive, she betrays Atilla's hospitality and causes the death of her siblings, along with Hagen, the assassin.