Jormungand (pronounced "YOUR-mun-gand"), also known as the World Serpent, is a sea serpent and child of Loki and Angrboða. Odin took Loki's three children by Angrboða, Fenris Wolf, 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.
Magnus Chase and Samirah al-Abbas get Jormungand's attention (further intending to get the attention of Ran) by throwing a bull's head into the ocean. He threatens to completely wake up and destroy the world.
In The Sword of Summer, Jormungand is described as a gigantic serpent with his scaled hide glistening in a camouflage patchwork of green, brown and yellow. His ridged forehead and tapered snout make him look more like an eel than a snake, however. His eyes resemble huge green spotlights the size of trampolines, while his irises glow so intensely, that Magnus was certain that everything he saw for the rest of his life would be tinted the colour of lime jelly.
When Jormungand opened his mouth, the stench of serpent poison was so strong that Magnus' clothes smoked. The serpent's teeth gleamed in rows of perfect white triangles, with his pink maw being big enough to swallow Harald’s 20-foot-long boat and a dozen of Harald’s closest friends’ boats simultaneously.
- During Ragnarök, the World Serpent is destined to be killed by Thor, yet his venom will also kill the latter shortly thereafter.
- His Egyptian equivalent is Naunet who is also depicted as a giant sea snake surrounding the world.
- His Greek counterpart is Keto.