Jörmungandr is one of the sons of Loki and the giantess Angrboda. Just like his siblings, he possesses tremendous power. He shares two common traits with his brother Fenrir: his animal shape and his continuous growth in size.
Jörmungandr takes on the shape of a snake. When the Norse gods find out about his existence, they decide to cast him into the ocean that surrounds Midgard. This is where he lives out the rest of his days, growing larger and larger by the day. At one point in time he grows so large that his body completely surrounds the boundaries of Midgard. This is how he earns the nickname, the Midgard serpent.
His capacity to kill is impressive, as he has both enormous strength and an ability to spit deadly venom. He proves his strength by giving Thor and the giant Hymir a hard time on a fishing trip, during which the god of thunder and strength hooks the serpent on a fishing line. Their rivalry will end in a stalemate during Ragnarok, as Jörmungandr is killed by the god of thunder. Yet before the god is able to walk away from the battlefield, he dies in a pool of poison.