Fenris the wolf is the son of Loki and Angrboda. In the Lore he is prophesied to help destroy the world at Ragnarok, so the gods bind him.

Fireverse Fenris and Jormungandr have beast shapes because Loki is a shape shifter. In the Fireverse, Odin is aware of the prophecy about Fenris, and that is the main reason he gives Fenris to Tyr and Zisa to raise, to try to keep Fenris under control. Zisa already has an affinity for dogs because Fireverse Zisa is the same goddess as Nehallenia. Tyr and Zisa raise Fenris in their home as their foster son. It is a great tragedy when the gods decide Fenris has gotten too big—in the way that Ymir got too big, so that allowing him to keep growing would mean he would eventually eat the whole universe—and they decided to bind Fenris. The main person behind the decision to act when they did was Odin. Fenris regards his binding as a betrayal by his father figure Tyr. Fenris still loves Zisa but he is permanently mad at Tyr. Zisa still feeds Fenris; she catches fish in her nets in her fishing boat (she no longer sails her war boat) and brings them to his island where he is bound and she dumps her nets out on the beach, where he can just reach them.

Whether Fenris would have joined in the fight against the gods at Ragnarok if he had not been bound is a question about self fulfilling prophecy, but it’s irrelevant to the reason Fenris was bound. He would have devoured everything long before Ragnarok was supposed to happen otherwise.

Image: The Binding of Fenris by Dorothy Hardy, public domain via Wikimedia Commons