Brunnhilde is the fierce leader of the Valkyries, the sisterhood of warrior women who train in the branches of Yggdrasil and have severed their ties to men. She preaches a hard creed to her recruits, teaching that men serve only one purpose and should be discarded beyond it, and she takes Sif under her wing as a promising addition to the sisterhood.
Her contempt for the male sex is tested when Thor arrives seeking help. She takes the prince and his companions prisoner, dismissing his claims and accusing him of coming to reclaim the woman who fled him, and moves to have them executed for trespass. The attack of the Frost Giants changes the moment. Seeing the Asgardians fight, Brunnhilde relents, entrusting Sif to escort them safely home and telling her to return to the Valkyries only when she is truly ready.