The Fenris Wolf is one of the offspring of Loki and Angerboda, and was born with the appearance of a wolf.
The following tale is found in actual mythology and most other fictional versions of the Fenris Wolf. As the Fenris Wolf grew older, the Aesir determined that it would not be safe to allow it to roam free in Asgard, and began playing a game with it to see how easily it could snap the bonds of a rope they placed on it, but the wolf broke each rope. Finally, Odin had the dwarves forged and enchanted fetter from gleipnir, which is made of things that don't really exist, such as the roots of a mountain and the sound of a cat's paws. When the gods came to place it around him, the wolf suspected a trick, and said that it would only allow them to place the fetter around its neck if one of the gods placed his hand in his mouth as a gesture of trust. If the fetter proved unbreakable, he would bite the god's arm off. Tyr agreed to this, and when he found the fetter was unbreakable, he bit off Tyr's right hand. The Aesir then bound Fenris to the rock Gioll at the gates of Hel.
It is prophecized that at the time of Ragnarok, the Fenris Wolf will be unchained and devour Odin, then be slain in battle by Vidar.
The following stories are related to the Marvel Comics version of the character. All links are to the Marvel versions.
In Marvel comics, The Fenris Wolf attempted to steal the golden apples of Idunn away from her, but was driven off by Haakun the Hunter and banished to Varinheim.
he Fenris Wolf was unchained by Hela to assist in an attempt at bringing about Ragnarok, but the Ragnarok was thwarted by Thor and returned to his prison.
The Fenris Wolf was unchained again by Loki to join him, Ulik and Hyrm in an assault upon Asgard using weapons forged for them by Surtur. Ulik and Fenris attacked Thor in unison, and struck Mjolnir with such force that Sif's left arm was taken off in the blast. Hyrm then joined Ulik and the Fenris Wolf in battle, and together, the three of them shattered Mjolnir.
Thor returned to Asgard with his allies Captain America and Iron Man, who aided him against Loki's forces. Captain America saved Thor from the Fenris Wolf by throwing his shield into its open mouth. When he needed the shield back, Captain America kicked him in the stomach to recover it. Thor subsequently beat the Fenris Wolf badly, until it was shaking where it stood. Captain America frightened it off by crying "Ruff"!
The Fenris Wolf went on to assault Kurse, who was protecting orphaned children. Fenris slew him by plunging its hammer into his skull.
The Fenris Wolf participated in an assault upon Vanaheim, and again faced Thor in battle. Thor bound Fenris in chains and used its body to knock down Durok in order to save Sif.
After Thor had slain Durok the Fenris Wolf snapped its chains to face him again, but was quickly struck down by Beta Ray Bill.
Beta Ray Bill unleashed the power of his hammer Stormbreaker upon the Fenris Wolf and slew him, leaving nothing but his skeleton behind. At the sight of this, the armies that fought for the Fenris Wolf fled from Vanaheim.
Fenris returned to life to swallow Asgard's sun and moon, assisting to bring about Ragnarok, as Asgard perished.