Upon her marriage, Brunhild lost her supernatural powers and unhappily resigned herself to her union with Gunnar. When she discovered how she had been deceived, however, her smoldering resentment became outright hatred directed against Sigurd, the only warrior truly worthy of her hand. In one version of the myth, she instigated Gunnar and Hogni against Sigurd; in another variation, Gunnar himself was so jealous of Sigurd that he participated in the plot to kill his oath-brother.
After Sigurd's murder, Brunhild killed herself. Sigurd's widow, Gudrun, married King Atli of the Huns. Atli demanded that Gunnar and Hogni relinquish the Nibelung treasure, which they had hid. The brothers refused to give up the treasure, which Sigurd had won from the dragon Fafnir. In retaliation, Atli had Hogni's heart cut out, and then had Gunnar thrown into a snake pit to die in agony. Gunnar attempted to charm the snakes with a harp, but one adder resisted the enchantment and fatally bit him. In the Germanic epic 'Song of the Nibelungs' (Nibelungenlied), Gunnar is called Gunther.