In Norse mythology, Jörmungandr ("huge monster"), also known as the Midgard Serpent or Miðgarðsormr, is a sea serpent, the middle child of the giantess Angrboða and Loki. In the Prose Edda, 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. As a result, he received the name of the Midgard Serpent or World Serpent. When he releases his tail, Ragnarök will begin. Jörmungandr's arch-enemy is the thunder-god Thor.