In Norse mythology, Jörmungandr (Old Norse: Jǫrmungandr, pronounced [ˈjɔrmuŋɡandr̥], meaning “huge monster”, also known as the Midgard (World) Serpent (Old Norse: Miðgarðsormr), is a sea serpent, the middle child of the giantess Angrboða and Loki. According to the Prose Edda, Odin took Loki’s three children by Angrboða — the wolf Fenrir, Hel, and Jörmungandr — and tossed Jörmungandr into the great ocean that encircles Midgard. The serpent grew so large that it was able to surround the earth and grasp its own tail. As a result, it received the name of the Midgard Serpent or World Serpent. When it releases its tail, Ragnarök will begin. Jörmungandr’s arch-enemy is the thunder-god, Thor. It is an example of an ouroboros.
The major sources for myths about Jörmungandr are the Prose Edda, the skaldic poem Húsdrápa, and the Eddic poems Hymiskviða and Völuspá. Other sources include kennings in other skaldic poems. For example, in Þórsdrápa, faðir lögseims, “father of the sea-thread”, is used as a kenning for Loki. There are also image stones from ancient times depicting the story of Thor fishing for Jörmungandr.
Jormungand, also called the “Midgard Serpent,” is a snake or dragon who lives in the ocean that surrounds Midgard, the visible world. So enormous is he that his body forms a circle around the entirety of Midgard. He’s one of the three children of Loki and the giantess Angrboða, along with Hel and Fenrir.
The god Thor is his particular enemy. Two battles between them are recounted in the Eddas. In one, Thor fishes for Jormungand, and fails to pull him up only when the giant Hymir, terrified that this will bring about Ragnarok, severs the line, sending the snake back down to the depths. When Ragnarok does arrive, however, Thor and the Midgard Serpent are destined to slay each other.
Jormungand likely already featured in the religion of the original Germanic tribes, as evidenced by his existence in the later pre-Christian religions of different branches of the Germanic peoples. For example, continental Germans attributed earthquakes to his movements well into the Middle Ages.