What giant wolf swallows Odin during Ragnarok?

The giant wolf that swallows Odin during Ragnarök is Fenrir.

Fenrir is a monstrous wolf in Norse mythology and a child of Loki and the jötunn Angrboða. His rapid growth and the gods’ knowledge of prophecies about his future danger led the Æsir to bind him. The magical fetter Gleipnir finally holds him, but only after Týr places his hand in Fenrir’s jaws as a pledge; when the gods refuse to release the wolf, Fenrir bites it off.

At Ragnarök, Fenrir breaks free and joins the forces attacking the gods. He confronts Odin and swallows him whole. Odin’s son Víðarr then avenges his father by forcing Fenrir’s jaws apart and killing the wolf.

Fenrir is often confused with Jörmungandr because both are Loki’s monstrous children and both fight major gods at Ragnarök. Jörmungandr is the world-encircling serpent who battles Thor; Fenrir is the wolf associated specifically with Odin’s death.