Loki had three very special children with the giantess Angerboda. One was a really cute wolf puppy that he took to Valhal. Here it was allowed to grow up. The puppy was named Fenris.
But the Fenris vulture grew and grew, to a completely supernatural size. It became so large that even the gods were frightened, and they agreed to chain the Fenris vulture to better control it.
The gods had forged a chain so large and heavy that only Thor could carry it. The Fenris wolf was not thrilled to be chained, but Thor enticed: If Fenris could break the chain, he would become famous as the world's strongest wolf.
Then Fenris got the chain tied around his neck and he only tensed the muscles a bit before pieces of chain remnants flew through the air.
The gods tried with an even bigger and stronger chain, but just as much it helped.
Then I mingled: Magic had to be used to chain the Fenris vulture. I asked the dwarves to make a special chain, called Gleipner. It and had to be made of noise from cat paws, female beards, mountain roots, bear tendons, bird saliva and fish breath and was impossible to tear over.
But when Gleipner was done, Fenrisulven had become suspicious and would not be chained again.
Taurus was the only one brave enough to lure the Fenris vulture again. He promised that this would be the last test to test the wolf's strength. The Fenris vulture was very suspicious and only agreed to try the rope on one condition: As a pledge, Tyr had to put his arm in his mouth in the meantime.
But as the rope held and tightened around his neck, Fenris slammed his jaws together and Tyr lost his hand. But the Fenris vulture was now chained with Gleipner in a cave in Jotunheim. And here it remains to Ragnarok, where it will escape free, furious and out for revenge. Until then, it howls in the cave of rage.
To prevent it from snapping at the gods, they have put a sword across the gap on it. Fenris can therefore not close its mouth, and the foam forms a rushing river, which flows through Jotunheim.
As the Wolf's prediction later tells, the Fenris Wolf will fight the strongest ace gods at Ragnarok, and in this battle the Fenris Wolf will devour me, after which my son Vidar will throw my spear and kill the wolf.
The actual story of Taurus and the Fenris Wolf is found in Gylfaginning in the younger Edda. It is mentioned in Loki's quarrel in the older Edda.