Fenrir, also known as Fenrisúlfr, is the most famous wolf in the Norse Pantheon. The child of the God (not giant) Loki and the giantess Angrboda, his siblings are the great sea serpent Jormungandr, and of Hel, Goddess of the underworld.
When Fenrir was young, the Gods decided to raise him with them, for he was fast, strong and smart. As time passed the Gods saw how quickly Fenrir was growing and how ravenous - and destructive - he was. Fenrir grew to an epic size and his open jaws could reach from the ground to the sky. The more he grew, the more his appetite grew and more destructive he became, until the day the Gods decided enough was enough and that they should bind him, else Fenrir would destroy the nine realms.
The binding of Fenrir
Binding Fenrir was no easy. The great wolf was incredibly strong - and gigantic - possessing a fierce intelligence. Twice the Gods attempted to restrain Fenrir with chains they had made. Twice they failed.
The first chain was called Leyding, which they convinced Fenrir to put on as a show of his strength, as he could easily break the chain. This was true, and Fenrir snapped it apart with a single sharp kick.
The second chain was called Dormi and was twice as strong. Fenrir barely felt the difference and broke it easily.
Desperate for a way to restrain the mighty wolf, the Gods asked the fabled dwarven smiths to forge a chain capable of holding Fenrir. Surely crafting a chain capable of binding Fenrir would not be beyond their skill of the dwarves, the renowned master smiths responsible for creating weapons of legend such as Odin’s spear Gaugnir and Thor’s Mjölnir.
When the dwarves received the commission from the Gods, they immediately knew that simple metal would never hold Fenrir. To make Gleipnir, the impossible binding, they needed impossible ingredients:
The sound of a cat's footfall, the beard of a woman, the roots of a mountain, the sinews of a bear, the breath of a fish and the spittle of a bird.
While the first two chains were heavy and cumbersome, Gleipnir resembled a ribbon: thin, flexible and, most importantly, indestructible.
The Gods now finally had the means to bind Fenrir. However, having a leash and leashing a wolf are two very different things.
Brute strength would not be enough to bind Fenrir and the Gods knew it. They needed to fool Fenrir into the binding. Appealing to the wolf’s vanity, the Gods invited Fenrir to the isolated island of Lyngvi, and again challenged him to show his strength by putting on this new shackle, and then breaking free.
Fenrir has always been an intelligent creature. Despite, or perhaps because of the lightness of the “ribbon” he became very suspicious. He only agreed to participate in this “test of strength” if one of the Gods would put their hand in his mouth, as a show of good faith that they would not leave him imprisoned if he could not break the chain.
Naturally the Gods were reluctant to agree to this request. However, displaying courage and self-sacrifice, the God Tyr came forward and offered his hand to placate the wolf.
Fenrir allowed himself to be shackled by Gleipnir, holding Tyr’s right hand on his mouth. When Fenrir kicked, Gleipnir caught tightly, and the more Fenrir struggled, the stronger Gleipnir became. At this, everyone laughed, except Tyr, who had just lost his right hand in the jaws of the beast.
When the Gods were sure that Fenrir was fully bound, they took a part of Gleipnir called Gelgja (Old Norse "fetter") and ran it through a large stone slab called Gjöll (Old Norse “scream"). The Gods buried the stone slab deep into the ground and anchored it with a great rock called Thviti (Old Norse "hitter, batterer"). Fenrir reacted violently; he opened his jaws very wide, and tried to bite his captors. To avoid loosing more limbs to the wolf, the Gods wedged a sword into his mouth. Its hilt touched the lower jaw and its point the upper one; by means of it the jaws of the wolf were spread apart and the wolf gagged.
Enraged by this treason, Fenrir began to howl, a lament heard on all corners of Midgard. Being wedged open in this way, huge amounts of drool flowed from Fenrir’s mouth, which formed a river which the Norse called Ván (Old Norse “hope”).
Despite the Gods having full knowledge of the prophecy that one day Fenrir would cause the death of Odin, they refused to kill him. One might say that they didn’t kill him out of respect for their holy places, including the island, and that they did not want to taint it with the wolf’s blood.
Another possibility, much more likely, is that the Gods knew that their fate - Wyrd - was already determined by the Norns, and that slaying Fenrir would only make the death of Odin to come faster, as their destinies were inseparably connected in the end.
Fenrir and Ragnarök
Despite being fettered, somehow Fenrir managed to have two offspring, Hati and Skoll, who endlessly chase the moon and the sun across the skies. During Ragnarök they will finally catch their preys, causing never-ending darkness to spread on the nine realms soon before joining his father.
During the Ragnarök, the cosmos will be shaken by earthquakes, loosing the bindings of Fenrir and destroying the rock to which he is anchored, finally allowing Fenrir to break free from Gleipnir.
Free, Fenrir and his offsprings will rampage through the nine worlds, devouring everything before them. When Fenrir reaches Asgard he will have his final reckoning with Odin, who will be slayed by the furious wolf.
Fenrir’s fall will come by the hand of Odin’s son Vidarr, who will have a magical boot allowing him to stand in Fenrir’s mouth without being devoured. This will allow him to use his mighty strength to kill the wolf by ripping its jaws apart.
Fenrir’s death will shortly be followed by the death of - almost - all things causing the end of the world as we know it.
However, that is a tale for another post.