Jormungand, also known as the Midgard Serpent and the World Serpent, is a character appearing in American comic books published by Marvel Comics. The character, based on the serpent Jörmungandr from Norse mythology, first appears in Marvel Tales #105 (Feb. 1952), in the period between the Golden Age of Comic Books and the Silver Age of Comic Books.

The Midgard Serpent debuted in Marvel Tales #105 (February 1952) and was later tied firmly to Marvel continuity in the Silver Age of Comic Books in Thor #127 (April 1966). As in Norse mythology, the Marvel version of the Midgard Serpent is the nemesis of the Thunder God, who has two encounters with the creature – the events based directly on mythology – in Thor #272-273 (June–July 1978).

An attempt to cheat the fatal prophecy made regarding a final battle between Thor and the Serpent occurred in Thor #274-278 (July–December 1978), although the creature returned in Thor #325 (November 1982-January 1983). A "larger than life" battle between Thor and the Serpent was depicted in Thor #379-380 (May–June 1987), with writer-artist Walter Simonson using a splash page to depict the creature's size, and then full pages to demonstrate the battle between the pair.

Although killed, the Serpent was resurrected in Thor #486-488 (May–July 1995), and featured in The Avengers vol. 3 #1 (February 1998) before reappearing in Thor vol. 2 #80 (August 2004).

The Midgard Serpent first appears when a scientist draws what he believes to be venom from a statue of the creature, the liquid becoming a deadly solvent.

In the realm of Asgard, the seer Volla makes a prophecy that Thor will battle the Midgard Serpent during Ragnarök after it surfaces from the ocean. He will succeed in killing it, but die from its venom immediately afterwards.

Thor has two encounters with the creature that reflect the Norse myths. The first is a visit to the castle of the Storm Giant Utgard-Loki, who excels in the use of illusions. Challenging Thor to lift his pet "cat", who in reality is the Midgard Serpent, Utgard-Loki is terrified when Thor lifts all but one of the cat's feet off the ground. The second encounter occurs when Thor decides to cheat fate and kill the creature. Taking a fishing boat with the giant Hymir, Thor uses the head of an ox on a chain to draw the Midgard Serpent to the surface of the ocean. Although the creature takes the bait, Thor is unable to deliver the killing blow as Hymir cuts the chain.

Being aware of the prophecy regarding his son's death, Asgard's king Odin cheats fate during a false Ragnarok by replacing Thor with a surrogate known as Red Norvell, who, after gaining the power of Thor and his hammer, dies battling the Midgard Serpent. The Midgard Serpent reappears briefly when a group of Odin's enemies feed the Golden Apples of Idunn, intended for the Norse gods, to the creature, intending to weaken the gods before an attack. It is used as a bridge by Tyr and Loki's army. Thor imprisons the creature and forces it to return the apples.