Simon Cowell, the acerbic Brit who has helped give "American Idol" some of its sharpest _ and nastiest _ moments, will leave the popular singing show after this season.

The cantankerous judge said that "The X Factor," a show he created and is a hit in Britain, will join Fox's schedule next year. Cowell will be on "The X Factor."

Cowell's decision is the biggest threat yet to what has been the country's most popular TV program and a true cultural force. This season, original host Paula Abdul has been replaced by Ellen DeGeneres.

But Cowell, with his caustic commentary, has long been seen as the big star of "Idol."

He said it would have been difficult for him to do both shows. While he makes a reported $36 million a year to be on "American Idol," he owns "The X Factor" and could make much more if the show takes off.

Cowell and top Fox executives made the announcement to reporters in Pasadena at a meeting of the Television Critics Association, saying they had reached an agreement only a few hours before.

"I was offered a lot of money to stay on," Cowell said. "But that wasn't the reason behind it. I wanted to do something different. I wanted a new challenge."

Peter Price, chairman of the Fox Broadcasting Co., would not speculate on possible replacements for Cowell.

"We have to take our time on that," Price said. "We have to make sure the chemistry of the judges is as good as it can be."

Cowell said he didn't want to leave "American Idol" at a time when it was fading in the ratings.

"You want to leave on a high," he said. "I'm very proud of what the show has achieved."

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AP Television Writer David Bauder contributed to this report.