Jormungand is the son of Loki and Angrbod and the brother of Hel and Fenris.
Thor against Jormungand
Original Mythology[]
Though in the book Jormungand is both the World Serpent and the serpent at the roots of the World Tree, in the original mythology this was not the case. He was born to Loki and Angrbod, and, like his siblings, was presented to the Gods. When the Gods placed Hel in charge of Niflheim, and chained Fenrir on an island, they cast Jormungand into the sea. There he grew large enough to encircle the world. The serpent that eats at the roots of the Yggdrasil is Nidhogg, a completely separate being.
In Runemarks/Runelight[]
In Runemarks, Jormungand spends much of his time in Netherworld. He is set free as part of a plan to get the Aesir out of Netherworld.