Cartman wears a light blue and yellow ski cap, a red jacket, yellow gloves, and brown pants. He has light brown hair, which has been regularly seen since late in Season 5 (his hair magically turns black whenever he wears his Adolf Hitler outfit). He has a double chin, and is often made fun of because of his obvious weight problem.

According to creators Trey Parker and Matt Stone, when they were creating South Park, they were upset that "nowadays, it would be impossible to put a character like Archie Bunker on TV." But they thought that if he was an animated eight year old boy, it might just be allowed. Thus, Cartman was born.

It should be noted that Cartman's personality has changed significantly over the series. While always being self-centered and racist, it seems that in the first two seasons of the show he was portrayed as the fat, juvenile, unintelligent and immature bully with a much raspier voice. It seems that since then he has matured a lot more, with a more aggressive and racist personality. He also seems to be more manipulative with other people, and less naive on political and social aspects of the world, that the earlier Cartman would never be aware of.

Eric, who is usually only addressed by his last name or weight-related
nicknames (only his mother, and his teacher Mr. Garrison address him as Eric), is spoiled, foul-mouthed, ill-tempered, insensitive, anti-Semetic, racist, and openly contemptuous of the few who can stand his deviant behavior.

A recurring joke throughout the series is that despite the seeming sweetness and surface wholesome appearance of his 'mother', she is, in fact, a promiscuous, hermaphroditic, crack-smoking porn queen, prostitute, and overall degenerate. Typically, she dotes on her son endlessly, beyond simply spoiling him. Cartman can almost always get what he wants simply by whining. Then again, his bad attitude may possibly be genetic, as all of his other relatives appear to have exactly the same temperament as Eric himself (except for his good counterpart from an evil parallel universe). His attitude could also be explained by the environment he was brought up in, as when the children had to use Clyde as a 'replacement Cartman' because the real one was in jail for hate crimes, Clyde became as bad tempered as Cartman in the short amount of time he was subjected to the teasing of others, implying that Cartman acts the way he does as a sort of defense mechanism.

As the fat anti-hero of the four lads, he was never intended to be the focus of the series, but within the first season he captured the popular imagination more than his three friends Stan Marsh, Kyle Broflovski, and Kenny McCormick. The more outrageous and shocking his behavior, the more audiences seem to love him. Another reason for his apparent popularity is that Cartman tends to be the most pro-active of the four main characters. He is frequently the one to come up with new ideas and plans, usually told excitedly to his (often unimpressed) friends after running up to them and breathlessly shouting "You guys! You guys! Guess what?"

The show's writers do seem to be careful to treat the many unfavorable aspects of Cartman's behavior with contempt and Cartman is often shown receiving the brunt of consequences generated by his behavior. For example, although Cartman frequently insults and taunts his "friends", especially Kyle, Kenny, and Butters, he sometimes appears to be more cowardly than they are when it comes to physical confrontation. In "It's Christmas in Canada", Kyle slaps him and Cartman immediately bursts into tears. In "Christian Rock Hard, he provokes Token with racial jibes and Token easily beats him up, and in several episodes he is unable to overpower Kenny. This though usually depends on the scenario, as in the earlier episodes such as "Damien," "Spooky Fish" and "Tweek vs. Craig," Cartman has no problem with fighting the other boys back physically.

His peers also give as much as they take, constantly calling him "Fat Ass" and intimating that they like him the least.

Frequently, Cartman will come up with an idea (often one he bets on with Kyle) that sounds ridiculous, stupid, or even racist, but that initially proves to be true. However, while Cartman appears to initially take the upper hand, and his stupid/racist ideas seem to be taken as true, he inevitably gets screwed over at the end of the episode. This has happened, for example, in Red Hot Catholic Love (he initially is thrilled at having beaten Kyle in a bet, but becomes furious when Kyle is not crushed) and Christian Rock Hard (where he wins a bet that he could sell a platinum album as a Christian band, but then discovers that Christian music has no platinum sales rank). Therefore, in the end, Cartman almost always loses (though there are exceptions, such as in Die Hippie, Die).

It has been repeatedly hinted that Cartman has serious behavioral and emotional problems and/or gender issues. It may be from his mother being a hermaphrodite, and/or not growing up with a father. He exhibits several compulsive behaviors, including the need to complete singing the Styx song "Come Sail Away" if someone sings the start, and humming other prog-rock songs (including singing Asia's "Heat of the Moment" during a Congressional hearing on stem cell research). He also seems to enjoy humming the Carson Era theme song to The Tonight Show and the Dawson's Creek theme when going about doing dull tasks. He also subconsciously mimics the line "they mostly come at night... mostly," from the 1986 Aliens movie. He occasionally has tea parties with stuffed dolls, pretending they're talking about how cool he is, and on one occasion was seen re-enacting a scene from The Silence of the Lambs as Buffalo Bill videotaped him dressing up as and pretending to be Britney Spears by dancing round a cardboard cut-out of Justin Timberlake.

Although quite naive and often wildly misinformed (he once thought dolphins lived in igloos), and frequently characterized as a "fat retard", Cartman has been known to formulate complex plans that have succeeded. In I'm a Little Bit Country, instead of studying, Cartman records various documentaries on the American Revolution on a TiVo and then electrocutes himself with it in a tub, which sends him on a flashback/time travel experience to 1776.

Cartman also has an evil habit of appearing in peoples' houses in the middle of the night, scaring the occupants silly. He frequently does this to Kyle (possibly entering via a hole in the ceiling he created in the episode "Mecha-Streisand"), but has magically appeared in Butters' room (in the episode "The Death of Eric Cartman"), possibly after stealing a copy of the key to his house while disguised as Awesomo; Cartman may also break into peoples' houses with his "Mission Impossible Breaking and Entering Playset."

A defining character trait of Cartman is his single-mindedness when pursuing his life long goal of making $10 million. The schemes he has tried include starting a church and collecting donation money and starting a boy band called "Fingerbang" (Cartman doesn't realise the sexual innuendo — he says he overheard the term on HBO and assumed it described imitating a firearm with one's finger). He also appears to be driven by a desire to outdo Stan, Kyle, and Kenny, and often lays down challenges and bets to them, such as building a bigger tree house and recording a platinum album. In one episode Kyle deliberately congratulated Cartman on winning a bet, which of course ruined all of Cartman's egotistical satisfaction at having humiliated his peers.

Cartman is extremely anti-Semitic and racist. He frequently appears to be determined to eradicate Jews (though Kyle is, of course, Jewish). In the episode "The Passion of the Jew", he sees The Passion of the Christ and thinks it is Mel Gibson's way to rally people against the Jews. He dresses up as Hitler and organizes people in his anti-Jew march; they think it is a march trying to raise awareness for the movie, and Christianity, and that the German lines Cartman gives them to chant in the march, "Es ist Zeit f�r Rache" (It is the time for revenge) and "Wir m�ssen die Juden ausrotten" (We must exterminate the Jews) are actually Aramaic. However, he does like Chef, who is black.

Cartman's b�tes noires throughout the show have been hippies, whom he despises for a variety of reasons, maybe the biggest reason being because of Cartman's Conservative views. The show drops frequent hints that Cartman gets many of his attitudes from his mother.

Cartman has some redeeming qualities: he has saved the boys, the town, and the entire world on a few occasions. In the episode "Rainforest Schmainforest", Cartman's hatred of the rainforest saves the boys and the choir group, Getting Gay with Kids, from the fictionalized violent native people of Costa Rica. In the full-length movie, South Park: Bigger, Longer, and Uncut, his filthy mouth, coupled with the experimental V-chip implanted in his brain to stop him from swearing, saves the world from Saddam Hussein. He destroyed the Taliban and set up Osama bin Laden's death in "Osama Bin Laden Has Farty Pants". More recently, in the episode "Die Hippie, Die", his intolerance of hippies saves South Park from a hippie music festival, and more recently, in "Best Friends Forever", in an ironic twist, he saved the world from a gruesome Armageddon by going to the Supreme Court and acquiring the rights to pull out Kenny's feeding tube so that he can get his hands on a PSP, whereas Kyle and Stan try to save him by bringing the media to save his life because they believe those are Kenny's wishes, an obvious parody of the Terri Schiavo sensationalism that was going on at around the same time the episode aired.