The character first appeared as Cletus Kasady in The Amazing Spider-Man #344 (Mar. 1991) and as Carnage in The Amazing Spider-Man #361 (Apr. 1992).
Cletus Kasady is a psychopath and a homicidal sadist. Kasady is a deeply disturbed individual with a dark past: as a child, he killed his grandmother by pushing her down a flight of stairs, tried to murder his mother by tossing a television into her bathtub, and tortured and killed his mother's dog. After the latter, his mother then tried to kill Cletus, and was apparently beaten to the brink of death by Kasady's father, who received no defense from Kasady during his trial. As an orphan, Kasady was sent to the St. Estes Home for Boys, where his antisocial behavior made him the target of abuse from both the other orphans and the staff. Kasady gained revenge by murdering the disciplinarian administrator, pushing a girl (who laughed at him for asking her to date him) in front of a moving bus, and burning down the orphanage. It was during his brutal years at St. Estes that Kasady acquired his philosophy that life was essentially meaningless and futile, that "laws are only words", and came to see the spreading of chaos through random, unpatterned bloodshed as "the ultimate freedom."
Kasady became a serial killer. He was then captured and sent to Ryker's Island prison for 11 murders—though he bragged of a dozen more—where he shared a cell with Eddie Brock, who had lost the alien symbiote that transformed him into the supervillain Venom. Brock's symbiote soon returned and bonded with him again, and unwittingly left behind the symbiote's offspring. The new symbiote then entered Kasady's bloodstream through a cut and bonded with his blood, transforming him into Carnage. He escaped prison, and began a series of murders, and at the scene of each crime, wrote "Carnage" on the walls with his own blood. He was found by Spider-Man, though the hero proved to be no match for Carnage's powers. In desperation, Spider-Man made a truce with Venom to fight Carnage. Carnage was defeated with sonic weaponry, but the symbiote lived on because it is merged with Kasady's bloodstream.
Kasady is taken to The Vault, a prison for super-villains—then Ravencroft Institute, a facility for the super-human criminally insane. A doctor at the facility, hoping to find a "cure" for his madness, draws blood from him—unwittingly enabling Kasady to morph into Carnage—who goes on to recruit an army of psychopathic supervillains including Shriek, Demogoblin, Carrion, and Doppelganger to take over New York City. Using Shriek's "psychic channel" powers, he also drives ordinary New Yorkers to attack one another. Carnage and his "family" are ultimately driven back by Spider-Man, Venom, and a number of other superheroes and super-antiheroes, with Carnage and Shriek being remanded to Ravencroft.
During a subsequent jailbreak, he made it his mission to kill his only childhood friend, Billy Bentime—hoping to refute the notion that friendship should be paid in kind. Carnage nearly defeated Spider-Man until Bentime tricked Carnage into reverting to human form, enabling Spider-Man to knock out Kasady with a simple punch.
The Carnage symbiote was supposedly destroyed in a subsequent conflict, and Kasady was sent back to Ryker's Island, where he unexpectedly transformed during transfer and rampaged through the prison. Shriek, who was still in league with Carnage, aided Carnage in taking over the island and recruiting villains like the Abomination, Mysterio, Screaming Mimi, and the Lizard. His true intentions were to use a less potent variation of gamma radiation that was being developed on the island by S.H.I.E.L.D. to make himself the "ultimate killer", but was thwarted once again by Spider-Man. Though bonded to Cletus Kasady's bloodstream, the symbiote found a way to ditch its host by travelling through the institute's water pipes, overwhelming Ravencroft's chief, John Jameson, and using him to commit further murders. It eventually transferred itself to Spider-Man—Ben Reilly (Peter Parker's clone) at the time—when Ben bonded with it in order to prevent it hurting any innocent people, creating Spider-Carnage. Ben's willpower held out against the symbiote's murderous desires long enough for him to return it to Ravencroft. Reilly subsequently attempted to destroy the symbiote by subjecting himself to a potentially lethal blast of microwaves, but it escaped back to Kasady after the microwaves forced it to separate from him.
During a subsequent rampage, the Carnage symbiote briefly attempted to take control of the Silver Surfer, who was visiting Earth at the time to welcome the Fantastic Four after their return to life following the battle with Onslaught. The Surfer and Spider-Man were able to return the symbiote to Kasady, and the Surfer then sealed Kasady in an unbreakable prison in an attempt to force him to reflect on his sins for eternity.
Having tracked Kasady to a prison specially designed to hold him—how he escaped the Surfer's prison has yet to be established—Venom eventually reabsorbs the Carnage symbiote into his own body "for good." Without the symbiote, Kasady attempts to re-assume the Carnage persona by costuming himself in red paint and continuing his killing sprees, claiming that he still possesses at least some of Carnage's strength and convinced that he only needs to kill Spider-Man and Venom to regain his symbiote, but Spider-Man nevertheless easily defeats him in a fight. Kasady, however, eventually finds another symbiote who had been kept sealed in the Negative Zone, and bonded with it to form the second Carnage.