Jormungandr

In Norse mythology, Jörmungandr (Old Norse: Jǫrmungandr, lit. 'the Vast 'gand'', see Etymology), also known as the Midgard Serpent or World Serpent (Old Norse: Miðgarðsormr), is an unfathomably large and monstrous sea serpent or worm who dwells in the world sea, encircling the Earth (Midgard) and biting its own tail, an example of an ouroboros. As a result of his surrounding Midgard (the Earth), the beast is referred to as the World Serpent. Jörmungandr releasing his tail is one of the signs of the beginning of Ragnarök.\n\nJörmungandr is said to be the middle child of the god Loki and the jötunn Angrboða. According to the Prose Edda, Odin took Loki's three children by Angrboða – the wolf Fenrir, underworld ruler Hel, and the serpent Jörmungandr – and removed them from Asgard (the world of the Æsir). The serpent Jörmungandr was tossed into the great ocean that encircles Midgard. There the serpent grew so large that he was able to surround the Earth and grasp his own tail. The old Norse thunder god, Thor, has an ongoing feud with Jörmungandr and the two can be seen as archfoes. During Ragnarök, Thor and Jörmungandr will fight each other to the death.

https://en.wikipedia.org/wiki/Jormungandr