Fenrir is known to be a monster in the shape of a wolf. He is the Eldest child among his two other siblings, and was born to Loki and Angrboda. The gods had learned of his prophecy of being responsible for the destruction of the world, and locked him up in a cage. The only one who was brave enough to care for and feed the wolf was Tyr, the god of War.
When Fenrir grew in size, the gods all thought he was weak and so they doubted he was strong enough to break the chains binding him. Fenrir accepted this challenge, and broke through them with ease. The gods then turned to a magical chain fashioned from six strange materials by the dwarves (crafty little creatures, they are). Those materials consisted of fishes breath, a cats footstep, roots of a mountain, a woman's beard, the sinew of a bear, and a bird's spittle. The magical chain, Gleipnir, was so thin and soft that many would doubt it's strength. Fenrir was less eager to break the chain, he said there was no pride in breaking such a chain. Fenrir agreed, though suspicious of treachery, he asked for the gods, as a token of good will, to place a hand between his jaws, and only Tyr agreed. Fenrir struggled with the thin chain, and no matter how hard he tried, he could not break it, so he bit off Tyr's hand in an act of revenge.
The gods, being very pleased with the results, carried fenrir off and tied him to a rock, Gioll, which was a mile within the Earth. They then put a sword between his jaws to keep him from biting. On the day of Ragnarok, Fenrir will break his chains and join the giants in their battle against the gods. He will seek out Odin, and devour him. Vidar, Odin's son, will avenge him by killing him.
Other names: Fenris, The Fenriswolf