Brunhilde was a mighty female warrior, one of the Valkyries. She was also a heroine from the German epics, especially in the Nibelungen saga, in which she is an Icelandic princess.
She defied Odin and in punishment he imprisoned her within a ring of fire on earth. She had to stay there until someone rescued her. Siegfied (Sigurd) braved the fire, woke her, and fell in love with her.