Both Alberich and Wotan want to get their hands on the ring again, and for this purpose both father children who are supposed to win the ring back for them. The Wälsungen - Siegmund and Sieglinde - and nine daughters, the Valkyries come from Wotan.
When Wotan realizes that Siegmund is not free and independent enough to win the ring, he orders the Valkyrie Brünnhilde to take care of Siegmund's death. She defies the order, but cannot prevent Siegmund's death. As punishment, Wotan puts her into a magical sleep on a rock protected from fire.