Grímhildr

Grímhildr (Old Norse for "masked battle") is one of the main antagonists in the Vǫlsunga saga. She was a beautiful but evil sorceress who was married to king Gjúki of Burgundy and had 4 children: Gunnarr, Hǫgni, Gutþormr and Guðrún.

Story
Queen Grímhildr gave Sigurðr a magic potion that made him forget that he ever married his wife Brynhildr, so that he would marry Guðrún, her daughter, while Brynhildr would marry her son Gunnarr. However, Brynhildr refused to marry Gunnarr, as she would only marry a man who could cross the ring of flames she put up around herself. So Grímhildr talked Sigurðr into helping Gunnarr marry Brynhildr. Since Sigurðr was the only one who could cross the flames, he and Gunnarr switched bodies, so Gunnarr's body could cross the flames. Brynhildr then married Gunnarr, because she made a promise. When Brynhildr learned that Sigurðr had betrayed her with Guðrún, not knowing he had been bewitched into doing so by Grímhildr, she was out to get revenge. She ended up killing Sigurðr and herself by the end of the saga. Grímhildr then made Guðrún marry Brynhildr's brother Atli. Guðrún did not want to marry him because she knew he would end up killing her brothers. This is the last mention of Grímhildr in the Vǫlsunga saga. It is probable that, in the original myth, the ring's curse also brought misfortune and even death upon Grímhildr herself.