A colossal sea dwelling serpent, the Jormungandr  may be the biggest beast in Norse mythology, and when you look at the tales of the other beasts, this really is impressive.
The name Jormungand is said to mean "Earth necklace" meaning, the beast is so large, the earth can wear it as a necklace and hold its tail in its mouth, in effect making it infinite; which drawers similarities with the Ouroboros.
Jormungand was said to be a child of Loki, along with Fenrir and Hel. Fenrir was a giant wolf, but was intelligent and vengeful. Jormungand was not much of a personality, and had little intelligence, which was lucky given the size and physical power of the beast.  Jormungand was hurled into the sea in anger when Odin found out about its existence, along with Fenrir who was outcast to an island, and Hel to the Underworld.
children of loki, jormungandr sea serpent
Like many Norse characters, Jormungand has found a place in many comic books, most notably Marvel’s Thor series. Other fantasy writers—including JRR Tolkein and Neil Gaiman—have been influenced by Norse mythology, including the giant serpent, as well.