Fenrir (Old Norse: Fenrir, also Fenrisúlfr, the Fenris-Wolf) is the monstrous wolf son of Loki and the giantess Angrboða, and one of the most cosmologically significant creatures in Norse mythology. The Æsir raised Fenrir among themselves in Ásgarðr, but as he grew to terrifying size they determined he must be bound. After two ordinary chains failed, the dwarves forged the magical fetter Gleipnir from impossible materials — the sound of a cat’s footstep, the beard of a woman, the roots of a mountain, the sinews of a bear, the breath of a fish, the spittle of a bird. Fenrir allowed himself to be bound only when Týr placed his hand in his mouth as a pledge; when Fenrir found he could not break free, he bit off Týr’s hand.

Fenrir remains bound on an island called Lyngvi in the lake Ámsvartnir, with a sword wedged in his open mouth, until Ragnarök. At Ragnarök, he breaks free and runs with his upper jaw touching the sky and lower jaw on the earth. He swallows Odin and is subsequently killed by Víðarr.