In Norse mythology, one of Loki's three children. Fenrir is a wolf. The Aesir tied him up with a magic rope, because they correctly assumed any offspring of Loki's would have to be evil. After Fenrir broke two normal chains, the gods promised they would untie him if the new one held him. One of them (whose name I forget) put his hand in Fenrir's mouth to show the gods' good will. When the Aesir left Fenrir in the rope, he bit off the guy's hand. All the gods laughed.