The stars of the show are eight-year-old children at South Park Elementary. There's the fat one, Cartman - the spoilt, boorish son of a single mum. There's the Jewish one, Kyle - the A-grade student and butt of numerous anti-Semitic jokes. There's Kenny, the poor one, who mumbles from inside the hood of his anorak and is gruesomely killed in a freak accident each week. And there's Stan, who has a gay dog called Sparkie.
This unlikely foursome and a cast of oddballs - including a sex-obsessed black chef and a homicidal schoolteacher whose alter ego is a hand puppet - live in South Park, a small town in the Colorado Rockies. Badly drawn (the characters only move sideways) and foul-mouthed, the series's appeal lies in subversive storylines which provide a barbed look at dysfunctional America.
These kids are the ultimate victims of American culture - obsessed with UFOs, exploited by advertising and steeped in traditional American values.
Plots include the abduction of Cartman by cow-mutilating aliens who subject him to an anal probe; a hunting trip with a couple of Vietnam vets; and the "outing" of Sparkie. Sparkie, by the way, is played by George Clooney, in, the producers insist, perhaps his finest acting role.
"If South Park was live action it would have been banned in a week," admits James Baker, head of programming at Sky 1, which is to show the series. "It's very funny, gross TV, but with an extra dimension. It's also very, very clever - social satire with a very English sense of humour you don't see often outside the UK. Yes, it has elements which are deeply offensive. But at its most shocking it also offers its cleverest social comment."
The show, described by one reviewer as "Peanuts on acid", is already a cult in the US where it has aired on Comedy Central for the past six months. South Park is big. So far it has generated a staggering $26m in merchandising sales.
More staggering, however, is that when Seinfeld ends this spring, South Park is tipped to become one of the top three humorous shows in the US, after The Simpsons and King of the Hill. Adult animation is big and getting bigger and, for many in US TV, it's the place to find the hottest young writing talent.
Take King of the Hill, the story of a red-neck Texan family headed by Hank, a propane salesman. This show, originally commissioned by Fox to accompany smash hit The Simpsons in a super double bill, recently overtook The Simpsons in the US TV ratings. Its unique combination of fantasy and hard-edged reality is created by teams of 16 writers on each half-hour show.
This isn't just a cartoon, it's social sitcom. Only the "com" goes far further than anyone would dare in live action. The producers have created their own world, so they can bend the rules much further. Brutal satire and savage pathos are all the sharper for not having either a starry cast or canned audience laughter.
Animation is increasingly being used in primetime to explore previously taboo subjects like race, religion and poverty. "Animation gives you the freedom to do the kind of show you really want to do," says Carl Gorham, a British comedy writer whose adult animation tale Stressed Eric, about a single father with two kids and a crippling mortgage, launches this spring. "[This freedom] has a significant impact on your writing; you can push things much, much further."
It is easier to control the voice of an animation as it is less likely to be ruled by committee, he explains. Which is what has attracted some of the hottest young writers to create some of American TV's most innovative series.
Take Duckman, the story of an accident-prone, sexually frustrated widower who combines a day job as the world's worst private detective with a chaotic family life. This show boasts some of the wordiest scripts on TV and most of the comedy is verbal. Then there's Dr Katz Professional Therapist, about a mumbling psychiatrist with a tortuous family life whose celebrity patients have included Garry Shandling and Winona Ryder.
Robin, meanwhile, is set in the warped imagination of a twentysomething unemployed hip-hop fan who lives in a one-room apartment in a big city. Up-and-coming shows include Celebrity Death Match (episodes include Charlie Manson vs Marilyn Monroe); Downtown, an animation verite that features the voices of real-life East Village citizens, and Invasion America, an animated sci-fi drama from DreamWorks.
British broadcasters are enthusiastic about the genre, although remain unconvinced of the potential for these shows to be as big in the UK. Or, for that matter, for British adult animation - which already boasts grown- up series like Pond Life, Crapstone Villas and Aardman Animation's upcoming Rex the Runt - to ever be as subversive a force in the UK.
Colin Rose, who heads the BBC's animation unit in Bristol, said: "The British have different expectations of animation. We tend to concentrate on the quality of the visuals. The Americans go more for minimalist animation but very, very strong writing."
So, even before its UK launch with ripples already reaching the blue rinse brigade, cult success seems guaranteed for the denizens of South Park.