Unusual cameos that make The Simpsons rock!

Soon after its debut in 1989, animated series The Simpsons quickly became America's hippest, funniest television programme -- cartoon or otherwise.

Like few shows before it, and none since, The Simpsons tapped into the psyche of middle-class America, while simultaneously examining the absurdities of US political and popular culture.

And, over the years, the show actually grew to became a kind of compass by which one could gauge America's general direction.

So, to provide a dash of authenticity to its portrayals of Americana, The Simpsons has always welcomed, as guest stars, eminent personalities from all walks of life.

Famous politicians, musicians, actors, celebrities, scholars, and others have all lent their voices to the show, and in many instances allowed themselves to be entirely recreated in animation -- and even poked fun at!

Indeed, appearing on The Simpsons became a kind of cultural rite of passage for some of the world's biggest stars.

Let's take a look at some of the more unusual guest stars.

Right from the start, The Simpsons writers showed a penchant for hard rock and alternative music stars. In Season 3's celebrated episode Flaming Moe's, the band Aerosmith had a guest appearance, beginning the trends.

Since then, rock acts like The Ramones, Red Hot Chilli Peppers, Green Day, REM, Lenny Kravitz, Kid Rock, Tom Petty and others have been featured as themselves, usually lending their music to the cause.

Rock culture in general has played an important role on The Simpsons, and many episodes have been devoted to it.

For example, season 7 episode "Homerpalooza" examines -- and pokes fun at -- the prevailing youth counterculture at the time, and featured several notable musician guest stars, including The Smashing Pumpkins.

America reveres professional sports, and its top American football, basketball and baseball stars invariably become huge cultural icons.

The Simpsons has brought on board many of these cultural figures, leading to some truly classic episodes. In season 3's Homer at the Bat, nine professional baseball players, including Roger Clemens and Ken Griffey Jr, appeared as themselves, when nuclear power plant owner Montgomery Burns pays for their baseball services to win a silly inter-company softball game.

Others sports stars have appeared include NBA legend Magic Johnson, former NFL quarterbacks Johnny Unitas and Joe Namath, and American tennis stars Andre Agassi, Pete Sampras and Venus and Serena Williams.

Even Brazilian footballer Ronaldo has lent his likeness to The Simpsons!

In the 1960's and 1970's, America fell in love with British bands in a major way -- The Beatles, The Rolling Stones, The Who and others. Though their music has somewhat faded in popularity, their presence in popular culture endures.

And so The Simpsons continues to host them -- Former Beatles members Ringo Starr, George Harrison and Paul McCartney (and ex-wife Linda) have all appeared on the Simpsons. So too have Sting, U2, The Who, and the Rolling Stones' Mick Jagger and Keith Richards.

In its fifteenth season, the Simpsons actually did a full episode in the UK, called The Regina Monologues, which starred Tony Blair, JK Rowling and several British actors!

The Simpsons has always aimed to provide a slice, however warped and zany, of everyday Americana.

Guest stars like astronaut Buzz Aldrin, talk show Larry King (twice), Playboy publisher Hugh Hefner, comedian and television presenter Bob Hope and late night show hosts Johnny Carson, Jay Leno and Conan O'Brien have all done their part to add to The Simpsons authenticity in recreating this world.

On the flip side, always intelligent and with plenty of pithy references, the show has invited imminent thinkers like biologist Stepehen Jay Gould, physicist Stephen Hawking, author and political thinker Gore Vidal, and author and journalist Tom Wolfe.

Pop stars have long sat atop the throne of American culture, the very culture which The Simpsons aims to portray and poke fun at.

So it makes sense that pop stars, young and old, would appear on The Simpsons.

Musicians like Tony Bennett, Linda Ronstadt, Barry White, Bette Midler and Lionel Richie have all appeared. Younger artists, too, like Britney Spears and 'N Sync, have gotten in on the act.

But the most noteworthy appearance belongs to the late Michael Jackson, King of Pop, who voiced a character in season 3's Stark Raving Dad.

In the episode, Homer gets sent to an insane asylum, where he meets an inmate named Leon Kompowsky. Leon, voiced by MJ, is a large white man who claims to be Jackson, and even sings bits of two his songs!

Interestingly, it was Jackson, a huge fan of The Simpsons, who actually called up creator Matt Groening and offered to do a guest spot, pitching several show ideas.

Later accounts agree he was a great sport about the whole thing, and the episode is cherished by many fans for being an insight into a lighter side of the great, troubled musician.