What is the world serpent that encircles Midgard?

The story behind the answer

Jörmungandr, the Midgard Serpent, is the colossal sea serpent cast by Odin into the ocean that grew so vast it encircled Midgard and grasped its own tail. In Norse myth, it’s fated to battle Thor at Ragnarök: Thor slays Jörmungandr with Mjölnir but dies shortly after from its venom.

By contrast, Fenrir is a monstrous wolf, Nidhogg gnaws the roots of Yggdrasil, and Leviathan comes from Hebrew tradition, not Norse. Memory tip: Jörmungandr literally means “great serpent” (jormun = great, gandr = serpent/monster). Think “Jörmun-girdle” wrapping the world—a ring around Midgard you can’t miss.