On Sunday at 8 p.m. EST on Fox, The Simpsons will be airing its 450th episode. Entitled Once Upon a Time in Springfield, the episode will be followed by an hour-long documentary from Morgan Spurlock (Super Size Me), called The Simpsons 20th Anniversary Special in 3-D on Ice.

“I think we could do it for another 20 years, actually,” says Simpsons creator Matt Groening ,talking about the show tying the longest running show in history: Gunsmoke, a series that has recently been tied by NBC’s Law & Order. “Omigod! Another 20? We’ll TRY,” he chortled. “We’ll do our BEST!”

“What I love about The Simpsons is, it’s so collaborative,” says Yeardley Smith about the writing process for the show. Smith voices the precious Lisa Simpson. “The actors do a third, the animators do a third and the writers do a third. That’s how I see it.”

“Together with NFL football, The Simpsons put the Fox network on the map — whatever you think of that,” said Harry Shearer, who voices many roles on the show including Mr. Burns, Waylon Smithers, Ned Flanders, Reverend Lovejoy, Kent Brockman, Dr. Hibbert and Principal Skinner. “And Fox has changed the face of network television — you got to decide for better or worse. “I wish I could say that we inspired an awful lot of funny, smart, irreverent, acerbic shows that took a lacerating view of the institutions of society. But I don’t think we have.”

“Matt has a satirical, anti-authority streak,” says Shearer. “From the beginning, The Simpsons was taking the side of the family against all the authority figures and institutions that buffeted them in the modern world. Certainly, that resonated for me.

Shearer remembers the first script the series, whose characters assigned to him were highlighted in yellow. Most of the time, he didn’t see drawings of the new characters until months after he had created their voices, when the episode was finished: “Oh, THAT’S what he looks like!”

He adds “that after 20 years and 450 episodes,” Shearer sums up, “I don’t really think The Simpsons has increased the country’s skepticism about nuclear power.”

Here’s your chance to leave your legacy. Create a new character for one of television’s longest running shows, The Simpsons.

The Fox animated show will be giving one winner the chance to make a new character which will appear in an early 2010 episode featuring Coldplay’s Chris Martin.

Part of Fox’s 20th-anniversary celebration of The Simpsons, the contest is only for those 18-years-of-age or older and runs until 11:59 p.m. EDT October 24th. Submissions can be made online on the show’s official web site. Executive producer Al Jean wants the character to be “pithy and funny.” Jean will also help judge the characters along with series creator Matt Groening.

“It’s gotta be a human being. We’ve narrowed it down that much,” Jean said. The new resident of Springfield should be yellow and have the usual egregious overbite. Submitters must include the character’s traits, including his or her name/nickname; age; occupation; appearance and catch phrase(s). The winner will earn a trip to Los Angeles to work with producers and the show’s animation director. The winner will be announced in mid-November.

“We can’t thank them enough,” Jean said. “We’re now in uncharted waters: We’ve gone longer than any scripted show in prime-time history. It’s a cliche, but it wouldn’t be so except for these people who’ve loved the show all these years.”

The contest’s new character, which will be drawn by show’s animators, will appear in an episode in which Homer disappoints his wife Marge “by arriving late at a wedding after stopping to buy a lottery ticket. He encounters the new face while rushing to the ceremony, Jean said, adding that it’s possible the character could pop up on the series again.”

Fox has renewed The Simpsons through the 2010-2011 season, making the animated hit the longest-running series in prime-time TV history. The 44-episode pickup will bring the show to an astounding 493 episodes. Venerable Western drama Gunsmoke aired on CBS for two decades. The Simpsons aired its first regular episode in January 1990 after a 1989 Christmas special.

Producers for the Fox show recently made headlines when it was announced that Marge Simpson will be appearing in the November issue of Playboy.