In Norse mythology, Jörmungandr is the enormous serpent encircling Midgard and destined to fight Thor at Ragnarök.
Jörmungandr is also called the Midgard Serpent. Norse sources identify it as a child of the trickster god Loki and the giantess Angrboða, alongside Fenrir and Hel. Odin cast the serpent into the sea surrounding Midgard, where it grew until it encircled the world and grasped its own tail.
Thor and Jörmungandr are recurring enemies. In one famous tale, Thor nearly pulls the serpent from the sea while fishing with the giant Hymir. At Ragnarök, the serpent emerges from the ocean, releases its tail, and poisons the air before Thor kills it; Thor then takes nine steps and dies from the venom.
Jörmungandr is not the same creature as Níðhöggr, the serpent-dragon associated with the roots of Yggdrasil.