Jörmungandr

In Norse mythology, Jörmungandr (Old Norse: Jǫrmungandr, pronounced [ˈjɔrmuŋɡandr̥], meaning "huge monster"), often written as Jormungand, or Jörmungand and also known as the Midgard Serpent (Old Norse: Miðgarðsormr), or World Serpent, 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. Less important 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.

...
Wikipedia