Fenrir is the monstrous wolf born to Loki and the giantess Angrboða, raised for a time among the gods until prophecy warned that he would grow to bring them ruin. The Æsir resolved to bind him, but two ordinary chains he snapped as if they were thread. So the dwarfs forged Gleipnir, a ribbon made from six impossible things — a cat’s footfall, a woman’s beard, a mountain’s roots, a bear’s sinews, a fish’s breath, and a bird’s spittle — slender as silk but unbreakable. Fenrir, suspicious of a trick, agreed to be bound only if one of the gods would place a hand in his jaws as a pledge. Only Týr dared it, and when Fenrir found he could not break free, he bit the hand off.
Fenrir strains against Gleipnir, a sword wedged in his jaws to keep them open, until Ragnarök, when he finally slips his bonds and swallows Odin whole.
Þá kemr inn mikli mögr Sigföður, Víðarr, vega at valdýri. Lætr hann megi Hveðrungs mundum standa hjör til hjarta, þá er hefnt föður
“Then comes Sigfather’s mighty son, / Vithar, to fight with the foaming wolf; / In the giant’s son does he thrust his sword / Full to the heart: his father is avenged.” — Völuspá, tr. Bellows
Víðarr, Odin’s son, avenges his father by prying or tearing the wolf’s jaws apart, ending the line of Loki’s most fearsome child.