Gleipnir is its name. A chain wrought by dwarves. A marvel created from the sound of a cat’s footsteps, the beard of a woman, the roots of mountains, the breath of a fish, and the spittle of a bird. Things that do not exist. Therefore struggling against this magical chain is futile.
The gods commissioned the dwarves of Svartalfheim to make this chain because of a great wolf named Fenrir.
Fenrir is one of the children of Loki. Loki also fathered the Midgard Serpent and Hel, the mistress of the non-battle dead.
Fenrir is the youngest of Loki’s children but the most dangerous, therefore unlike Hel and the Midgard Serpent he was kept in Asgard, the kingdom of the gods and the god Tyr was his keeper.
Finally the gods realised the vicious Fenrir was growing unmanageably huge so they decided they would have to bind him to keep him from escaping and ravaging the world.
Fenrir was tricked by the gods to let them chain him by saying it was merely a test of his strength. He broke every bond easily. That is when the gods turned to the dwarves to create Gleipnir.
The Wolf was suspicious when the gods presented Gleipnir to be his next challenge as it seemed so light and supple, so he demanded that one of the gods rest his hand in his jaws so if the chain didn’t break and he wasn’t set free he would devour that hand. Tyr stepped forward, brave and stoic and placed his hand in the great wolf's mouth.
The chain would not break. Tyr lost his hand and the Wolf is bound under the roots of Yggdrasil until the time of Ragnarok, the world's end, guarded by the giant dog Garm. The gods placed a sword in Fenrir's mouth to keep his jaws open and he howls ceaselessly and from his drool comes the river Expectation.
During Ragnarok Fenrir will break the magical chain and Garm will howl a warning. Fenrir will devour Allfather Odin and in turn will be slain by Odin's son Vidar.