The magical chain that bound the wolf Fenrir is called Gleipnir.
In Norse mythology, the gods feared Fenrir because prophecies foretold that the monstrous wolf would eventually break loose and threaten the gods, including Odin. Two earlier restraints, Leydingr and Dromi, were massive iron fetters, but Fenrir tore through both of them.
The gods then commissioned dwarfs to make Gleipnir. Although it looked like a slender, smooth silk ribbon, it was stronger than any iron chain. According to the Prose Edda, it was made from six impossible ingredients: the sound of a cat’s footfall, a woman’s beard, mountain roots, bear sinews, fish breath, and bird spittle. Their disappearance explains why these things cannot be found in the ordinary world.
Fenrir agreed to be bound only if one of the gods placed a hand in his mouth as a guarantee that he would be released. Týr accepted the risk. When Gleipnir held and the gods refused to free the wolf, Fenrir bit off Týr’s hand. He remains bound until Ragnarök, when he is destined to break free.