Fenrir (Fenris)

Fenrir is also known as Fenris or Fenrisulfr. He is a giant wolf of Norse (Viking) mythology, and one of the children of the god Loki and the giantess Angrboda. He is much larger than a normal wolf, some tales claim he is even twice as large. As a result of his size he has been described as a monster. His father, Loki, is the god of mischief and trickery. As a result, his children have all been troublesome.
The gods heard of a great prophecy that involved Fenrir. The prophecy was that Fenrir would destroy the world with the help of his family. He would devour all in his path, and his two children would eat the sun and the moon. As Fenrir grew much faster than a normal wolf, the gods became very worried, and attempted to lock him in a cage when he was just a cub. Only the god of war, Tyr, dared to approach him and feed him.
When Fenrir was no longer a cub they had no choice but to free him. Yet, they were still worried about the prophecy about Ragnarok (the end of the world), as it involved Fenrir. They decided to chain him up in an attempt to prevent the prophecy from coming to pass. They realised it would be impossible to force him to submit, as he was too strong. Instead, they challenged Fenrir to break through a metal chain in order to prove his strength. Fenrir accepted the challenge, eager to show off and boast about his superiority. He easily broke free and laughed.
This left the gods in despair, but they did not give up. Instead, they went to the dwarves for help. They asked them to create a chain that could not be broken, and the dwarves came up with a giant ribbon. The ribbon was made from the footstep of a cat; the roots of a mountain; a woman's beard; the breath of fishes; the sinews of a bear; and a bird's spittle. They challenged Fenrir again, but he was reluctant, suspecting trickery from the gods. Eventually he agreed, but only because he feared the gods would think he was weak. He could not break free, and has remained there ever since.
At Ragnarok Fenrir will finally break free, and help destroy the world. He will swallow Odin, the king of the gods, before being killed by Odin's son.
For more information visit:

• http://www.mythicalcreaturesguide.com/page/Fenris+Wolf 
• http://en.wikipedia.org/wiki/Fenrir 
• http://www.pantheon.org/articles/f/fenrir.html 
• http://norse-mythology.org/gods-and-creatures/giants/fenrir/ 
• http://mythology.wikia.com/wiki/Fenrir