Loki secretly married a hideous giantess Angur-boda (anguish boding), who bore him three monstrous children: the wolf Fenris; Hel, the goddess of death; and Iormungandr, a terrible serpent.
Loki tried to keep the existence of these monsters secret as long as he could; but they grew so large that they could no longer be confined in the cave where they were discovered.
Odin soon became aware of their existence, and also of the disquieting rapidity with which they increased in size.
Afraid that the monsters could invade Asgard and destroy the gods, "Allfather" (Odin) decided to get rid of them by first throwing Hel into the depths of Nifl-heim, telling her she could reign over the nine dismal worlds of the dead.
Next, he threw Iormungandr into the sea, where he grew to such an immense size that at last he encircled the earth and could bite his own tail.
Noting that the serpent grew to such a fearful size in his new element, Odin decided to take Fenris to Asgard, where he hoped, that with kind treatment, the wolf would become gentle and be safely under control.
All of the gods were so afraid of the wolf that they would not go near him to feed him except Tyr, who was afraid of nothing.
Aware that Fenris was quickly increasing in size, strength, violence, and savageness; the gods assembled to decide how they could dispose of him.
They came to a unanimous decision to bind him so he could not do them any harm.
They found the strongest chain available and then challenged him to show them how easily he could break the chain after they put it around him.
Fenris was confident that he could release himself, so he let them bind him as much as they wanted.
When they stepped back, he stretched himself and easily broke the chain to the disappointment of the gods, but they loudly praised him for his great strength until they could find something else with which to confine him.
The gods realized that no ordinary bond, regardless of how strong it was, would ever hold Fenris.
Next, they asked the "dark elves" to use their magic arts to make something which nothing could break.
The dark elves used their magic arts to make a slender silken rope from such materials as the sound of a cat's footsteps, a woman's beard, the roots of a mountain, the longings of the bear, the voice of fishes, and the spittle of birds; and when it was finished they sent it to the gods with the assurance that no strength would be able to break it, and that the more it was strained the stronger it would become
Taking this thin rope, the gods again proposed to test his strength. Although Fenris had grown even stronger, he didn't trust the cord that looked so thin.
He refused to allow himself to be tied up unless one of the gods would agree to put his hand in his mouth, and leave it there, as a pledge of good faith, that no magic arts were to be used against him.
The gods would have nothing to do with this demand and they all backed off except Tyr, who seeing that the others would not comply with this condition, boldly stepped forward and put his hand between the monster's jaws.
The silken cord was fastened securely around Fenris' neck and paws, and when they saw that his efforts to free himself were useless, they shouted and laughed with their apparent victory.
Tyr could not share their joy because Fenris, realizing that he was unable to escape, bit off Tyr's hand at the wrist, which since that time was known as the wolf's joint.
The gods, in spite of the wolf's struggles, tied Fenris to a very large rock and opening his fearful jaws, Fenris made such terrible howls that the gods, put a sword into his mouth, the hilt resting upon his lower jaw and the point against the top of his mouth.
The myth states that the wolf was destined to remain securely bound until the last day, when he would burst his bonds and would be free to avenge the wrong done to him.
Meantime, since Tyr was deprived of his right hand, he was forced to use the maimed arm for his shield, and to utilize his sword with his left hand; but such was his dexterity that he slew his enemies just as he did before.
http://www.wordinfo.info/words/index/info/view_unit/3222It is also said that, when Fenris returns, he will be so big
that his upper jaw will tear up the heavens, which will make fire rain down on
the world. And that, when he breaks free, he will eat the sun.