Jormungandr

Jörmungandr is the Midgard Serpent (also World Serpent) who encircles the realm of Midgard. He is the son of the god Loki and the giantess Angrboða and brother of the great wolf Fenrir and Hel, Queen of the Dead. At Ragnarök, the Twilight of the Gods, he slays and is slain by the god Thor.

Fenrir, Jörmungandr, and Hel were living with their mother in Jotunheim, realm of the giants, when the gods of Asgard received a prophecy that they would cause trouble in the future and so Odin ordered them removed when they were still quite young. He hurled Jörmungandr into the sea, consigned Hel to the dark realm of the dead below icy Niflheim, and eventually had Fenrir bound to a rock on an island. Jörmungandr grew to such an enormous size that he encircled the world – which was envisioned as a flat disc - and held his tail in his mouth.

At the end of days known as Ragnarök, Fenrir would break free, Hel would supply him with an army of the dead, and Jörmungandr would release his tail and rise from the seas to join the forces of chaos in battle against the gods and their heroes. The gods would almost all be killed but would defeat their adversaries and preserve order which continued in the rebirth of a new world rising from the ashes of the old.