Norse mythology Jörmungandr the Midgard Serpent, or World Serpent, is a sea serpent. Odin took Jörmungandr, and tossed it 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. When he lets go, the world will end. Depicted on this design being fished by it's arch-enemy Thor using an ox head as bait.