The Simpsons reach a milestone: Sunday's episode is the show's 500th

On Sunday evening, millions of Americans will tune in to watch a television show do what only two others have done before: Fox's The Simpsons - which, more than any other program put the domination in the network's Animation Domination lineup - will mark its 500th episode.

Only Gunsmoke and Lassie aired more episodes, at 635 and 588, respectively.

"I never imagined this," creator Matt Groening told USA Today. "I thought it would be a hit with kids. I wasn't sure adults would dig it."

But dig it they have.  The show transcends generations, poking fun at, well ... just about everyone and everything, from presidents to everyday life.

Fox and the show's producers inked a new production deal for the show last fall which will carry the series for at least another 59 episodes after tomorrow night.

Will it continue even beyond that?

No one really knows, but producer Mike Reiss says there's no way they'll ever run out of ideas for it. "(It's) a show about the world," he said. "We'll run out of material the day the world stops being interesting."