Jormungandr

In Norse Mythology, Jormungandr, the world serpent, is Loki's second monstrous child. He was born as a small snake, but rapidly grew. To deal with him Odin threw him out of the sky, intending to kill the creature with the impact of landing it on Earth. However, he landed in the ocean and survived, growing so huge that he wrapped around the earth. There he stayed, preying on oceanic creatures, until Ragnarok, when he broke free. He then was swiftly killed by Thor, the thunder god, who split his skull with a giant hammer. Jormungandr had his revenge, though: his toxic breath killed Thor.