In Norse mythology, Fenrir (Old Norse: "fen-dweller"), Fenrisúlfr (Old Norse: "Fenris wolf"), Hróðvitnir (Old Norse: "fame-wolf"), or Vánagandr (Old Norse: "the monster of the river Ván") is a monstrous wolf. Fenrir is attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda and Heimskringla, written in the 13th century by Snorri Sturluson. In both the Poetic Edda and Prose Edda, Fenrir is the father of the wolves Sköll and Hati Hróðvitnisson, is a son of Loki, and is foretold to kill the god Odin during the events of Ragnarök, but will in turn be killed by Odin's son Víðarr.
In the Prose Edda, additional information is given about Fenrir, including that, due to the gods' knowledge of prophecies foretelling great trouble from Fenrir and his rapid growth, the gods bound him, and as a result Fenrir bit off the right hand of the god Týr. Depictions of Fenrir have been identified on various objects, and scholarly theories have been proposed regarding Fenrir's relation to other canine beings in Norse mythology. Fenrir has been the subject of artistic depictions, and he appears in literature.
I can never remember though, was it Fenrir or his children who would devour the sun and moon during Ragnarok?