The Fenrir Wolf is a creature in Nordic mythology. 

The Fenrir wolf is one of Loki's children. The æsir, a general definition of the gods in the Nordic mythology, tries to chain the wolf with an unbreakable chain, because it is so frightning. They ask the Fenrir wolf if they can put it on a chain to see if it has the strenght to break the chain.

However, the Fenrir wolf is rather cunning and demands that one of the gods should put their hand in its mouth as a security precaution. The æsir accepts the demand and the god Tyr puts his hand in the wolf's mouth. The æsir manages to chain the Fenrir wolf, but as revenge, it bites of the hand of Tyr. 

At Ragnanok (or Armageddon / end of the world), it is said that the Fenrir wolf will break loose of its chains and kill the god Odin in battle. The Fenrir wolf itself will afterwards be killed by Vidar, the son of Odin.