Fenrir

excerpt from article "Creatures in Norse Mythology" via Life in Norway

Fenrir

Another of Loki's delightful children, Fenrir the Wolf is the fiercest and most vicious of all the creatures. Thanks to prophecies noting Fenrir's growth and ferocity, the Gods decided he must be bound. They tried two strong chains, which Fenrir broke easily, before commissioning the Dwarfs to create Gleipnir. When the Gods came to tether Fenrir, he didn't trust them so the God Tyr places his hand in Fenrir's mouth as a bargain. After the Gods had bound him with Gleipnir, a tether that's as thin as silken ribbon but stronger than any chain, he reslised he'd been tricked and bit Tyr's hand clean off. At Ragnarok, Fenrir will kill Odin and then, in turn, be killed by Odin's son Víðarr.