Fenrir is a summon in the Final Fantasy series. His only Nintendo system appearance is that in Final Fantasy VI for the SNES and GBA, in which he takes on the appearance of a wolf (as he does in the PlayStation exclusives). In the video game, to summon Fenrir the player will have to use 70 magic points. Following this it'll use Image on the entire party. In the game, Fenrir will be obtained after the player defeats Humbaba for the first time.
In Norse Mythology, Fenrir is a giant wolf and one of the children of the magnanimous Loki. Because of the prophecy that Loki's children would become trouble, Odin sent out for them and brought Fenrir to the Eser to be kept in a prison where he would be bound for eternity until Ragnarök. The god became larger and larger and the Eser became frightful of him. During Ragnarök, Fenrir is destined to kill Odin.