This month marks the twenty-fifth anniversary of the first full appearance of the Spider-Man villain Carnage. Carnage made his first appearance in The Amazing Spider-Man #361 after a brief cameo in #360, though his alterego of Cletus Kasady debuted the year before in #344. He is one of the most dangerous villains in comics books. Cletus was a homicidal psychopath who saw bloodshed as "the ultimate freedom," but after bonding with the spawn of Venom he became significantly more dangerous. His threat was so extreme he forced rivals Spider-Man and Venom to team up to fight him. His most famous act was during the Maximum Carnage story, and video game tie-in, where he recruited numerous psychotic villains requiring dozens of heroes to fight them. Since then he has continued to pester Spider-Man and other heroes, though never quite to the same success, while also spawning a symbiote "son" of his own who became a hero that fought Carnage.
Due to his dangerous nature, Carnage has had limited exposure in animation. His first was on Spider-Man where he debuted in "Venom Returns" and "Carnage" voiced by Scott Cleverdon. While Cletus' homicidal nature was not stated, it was alluded to with a comment that he has done things no paper would report. Though brief, his appearances did follow the comics faithfully with Cletus being incarcerated next to Eddie Brock, teaming up to fight Spider-Man, and then turning into a bitter rivalry so Venom and Spider-Man team up to stop him. However, he was not allowed to do any killing, instead using a spell from Dormammu to suck the "lifeforce" out of people. A robot duplicate of Carnage later appeared for use by Mysterio in "The Haunting of Mary Jane Watson".
The series ended with Spider-Carnage. In this universe, Spider-Man bonded with a dimensional-traveling Carnage symbiote to become the ultimate villain as voiced by Christopher Daniel Barnes. This was based on a brief time in the comics when Ben Reilly bonded with the Carnage symbiote requiring Peter's help to rescue him. This character ended up destroy the Multiverse requiring Beyonder and Madame Web to turn back time and train various Spider-Men to combat this threat.
Michael Donovan was a recurring character on the much-derided Spider-Man Unlimited. In the loose sequel to the previous series, this version teamed up with Venom as part of the Synobtic who plan to take over Counter-Earth. The show ended with the two symbiotes unleashing their plan to create a planet of symbiotes under their control. This was the last time the original Carnage appeared in animation. His appearance and new powers were inspired by Venom in the 2099 comics.
While Carnage never appeared, Cletus Kasady did have an unvoiced appearance on The Spectacular Spider-Man episode "Reinforcement". This version is an inmate at the Ravencroft Institute for the Criminally Insane under the care of Dr. Ashley Kafka along with Otto Octavius and Max Dillon. It is likely that had the series gone on he would have become the symbiote-powered villain.
The opposite occurred for Ultimate Spider-Man where the Carnage symbiote appeared but Cletus did not. This version followed the Ultimate version of the character. The symbiote was first voiced by Dee Bradley Baker and later by Fred Tatasciore. It was first created in the episode "Carnage" by Green Goblin after he injected Peter Parker with part of the Venom symbiote to create a better version. Later, the symbiote bonded with Doctor Octopus and Hulk. In a storyline borrowed from the comics' Spider-Island, Carnage explodes himself so he infects every civilian and some heroes in New York City. The symbiote possesses Mary Jane Watson to become the Carnage Queen, in charge of the symbiote drones. She later uses a piece of the symbiote to become the next Spider-Woman and joins Spider-Man in saving the city.