Jormungand

Jormungand also known as the World Serpent is a sea serpent and child of Loki. Odin took Loki's three children by Angrboða, the wolf Fenrir, Hel, and Jormungand, and tossed Jormungand into the great ocean that encircles Midgard.

The serpent grew so large that he was able to surround the earth and grasp his own tail. As a result, he received the name of the World Serpent. Jormungand's arch-enemy is the god Thor.