NBC Universal chief Jeff Zucker, who rose from a youthful producer at the "Today" morning show to run the multifaceted media business, said he would step down after cable provider Comcast takes control of the company later this year.
The news came as Jonathan Klein, president of CNN, was fired and replaced by Ken Jautz, the head of the network's sister channel HLN.
NBC's Zucker told employees of his planned departure in an e-mail he sent Friday, and Comcast's chief executive said that he wished him well.
"It has been a great run and I've been incredibly fortunate," Zucker wrote to his colleagues.
The possible change-in-command had been looming since last December, when Comcast Corp. agreed to buy a 51 percent stake in NBC Universal from General Electric Co. That deal still hasn't cleared regulatory hurdles, but that is expected around the end of the year.
Klein was fired earlier this week by CNN's worldwide president Jim Walton. According to a report from the New York Times, Klein was told "they wanted to restructure things this way, and thank you very much, and good luck."
Klein was in charge of the U.S. network for nearly six years. But amid slipping ratings, media critics have questioned his ability to lead the network.
Zucker's work with NBC was also marred by slipping ratings for its prime-time lineup, from its 90s dominance (the "Friends"-era) to where it has been the fourth-place broadcast network. Yet, NBC News has remained the strongest broadcast news division and the network continues to dominate in late-night programming.
NBC Universal has done well financially with its owned networks; Zucker has said that NBC Universal is essentially a cable company now.
NBC Universal owns the NBC and Telemundo television networks along with 26 TV stations; cable channels USA, Bravo, Oxygen, Syfy, CNBC and others; the Universal Pictures movie studio and Focus Features; theme parks in California, Florida and Japan; and has part ownership of online video site Hulu.
NBC's experiment last season putting Jay Leno in prime time proved a spectacular failure, blowing up further when Conan O'Brien refused to move to a later time slot to accommodate Leno's return to the "Tonight" show.
CNN slipped behind MSNBC into third place this year in its prime-time ratings, where Fox News Channel remains a dominant number one.
The image of CNN as hurting particularly frustrates Walton, who noted that prime-time advertising accounts for only 10 percent of the company's revenue. CNN has been profitable for seven consecutive years during a disastrous time for the news industry, he said.
"CNN is not broken," he said. "While we're not satisfied with the ratings at CNN prime time and they clearly need to get better, CNN as an organization and a business is thriving."
Klein has held his job for six years, overseeing more aggressive news coverage and the development of Anderson Cooper and Sanjay Gupta as major personalities. The former CBS News executive said he's confident CNN is better today than when he arrived in December 2004.
The Associated Press contributed to this report.