Jormungandr, also called the “Midgard Serpent,” is a snake or dragon who lives in the ocean that surrounds Midgard, the visible world. So enormous is he that his body forms a circle around the entirety of Midgard. He’s one of the three children of Loki and the giantess Angrboda, along with Hel and Fenrir.
The god Thor is his particular enemy. Two battles between them are recounted in the Eddas. In one, Thor fishes for Jormungandr, and fails to pull him up only when the giant Hymir, terrified that this will bring about Ragnarok, severs the line, sending the snake back down to the depths. When Ragnarok does arrive, however, Thor and the Midgard Serpent are fated to slay each other.
Done with Sharpies!