Two veteran NBC executives, George Cheeks and Paul Telegdy, were named cochairmen of NBC Entertainment on Monday, replacing Bob Greenblatt at a time of upheaval in network television.

Greenblatt, who had been NBC's top programmer for nearly eight years, approached his boss, NBCUniversal chief executive Steve Burke, about two weeks ago and said he no longer wanted the job. The two finalized Greenblatt's exit over the weekend, and Burke swiftly installed new leadership at the Los Angeles unit, which includes the NBC network and Universal Television production studio.

"These are extremely challenging jobs, and there is a natural fatigue that sets in," Burke told the Los Angeles Times. "If you are not 100 percent ready for the challenge, then it is time to think about doing something else."

NBC's changing of the guard came on the first day of the new TV season and as management of all four major TV networks is in flux. Ben Sherwood is stepping down as Disney/ABC Television Group president as soon as the Walt Disney Co. completes its $71.3 billion acquisition of much of 21st Century Fox, according to two people familiar with the situation. Disney plans to officially announce that it is bringing over two Fox executives, Peter Rice and Dana Walden, to run ABC television, which will leave a gap at Fox.

And this month, there was a shake-up at CBS Corp. when Leslie Moonves was forced to step down as chief executive amid a sexual harassment scandal.

The broadcast business is vexed by declining ratings and increased competition for viewers' attention from video streaming services. Netflix, Amazon.com, and other deep-pocketed rivals have been assembling an arsenal of shows and wooing A-list show runners with lucrative contracts and promises of creative freedom without the pressure of having to produce giant ratings.

Neither Cheeks nor Telegdy is a household name, but they are familiar to Hollywood's talent agents and television producers as well as NBC's nearly 850-person workforce.

Burke said he had no interest in bringing in an outsider to run NBC. Cheeks and Telegdy, who have worked together for years as top lieutenants to Greenblatt, will share duties.

"One of the biggest legacies that Bob leaves is the strength of his team," Burke said. "We think the two of them will make a great partnership."

There have been several notable partnerships in the entertainment world, including that of Fox's Walden and Gary Newman. Those executives have worked together for about 20 years and currently are chief executives of the Fox Television Group, in charge of the broadcast network and TV studio.

Cheeks and Telegdy will share the responsibilities of the NBC Entertainment job, which includes overseeing prime-time entertainment, late-night programming, daytime shows, television production, scheduling, marketing, and research on the West Coast.

Telegdy, 47, has been one of NBC's top programmers since 2008, and until Monday he was president of the alternative and reality television group. He has been responsible for NBC's unscripted series and specials, including America's Got Talent, World of Dance, and American Ninja Warrior.

But it was The Voice, the remake of a popular show from the Netherlands, that gave Telegdy his cred at NBC. The show has been one of the network's top performers since its debut in 2011.

"That was the first building block of turnaround of NBC, and it was all Paul and his team," Burke said.

Telegdy, a native of Britain, is the son of a Hungarian political refugee who became a chemical engineer and a former British actress turned teacher. He began his career in television by selling shows overseas, then joined the BBC in programming. In 2004, he moved to Los Angeles to help the BBC expand its business in the United States and quickly sold Extras, a TV show starring the British comic Ricky Gervais, to HBO.

Cheeks, 53, came up through the ranks of business affairs at rival Viacom Inc., where he worked for more than a decade with such networks as Nickelodeon, MTV, VH1, and Logo. He joined Viacom in 1998 after practicing law at Loeb & Loeb and the entertainment firm Hansen, Jacobson, Teller in Beverly Hills, Calif.

This year, he became copresident of Universal Cable Productions, a division of NBCUniversal, while also juggling his NBC duties as president of late-night programming. He is a graduate of Yale University and received his law degree from Harvard Law School.

"George is very strategic, he is a great deal maker, and he understands and works well with talent," Burke said.

Cheeks, who is biracial and gay, also brings diversity to a role that has long been held by white men.

NBC finished the 2017-18 television season in first place in all key audience categories, boosted by its broadcast of the Super Bowl and the Winter Olympics in South Korea, both of which produced blockbuster ratings. The new TV season could prove more troublesome because the Comcast Corp.-owned network won't have those big sporting events. Instead, CBS will televise the Super Bowl, and Fox will air NFL Thursday Night Football, a franchise that NBC and CBS shared last year.

Greenblatt's resignation took effect Monday. He will segue into a consulting role and plans to help stage Hair, which is scheduled as NBC's live production next spring. Greenblatt led the charge to reintroduce live theatrical productions to network TV and helped return NBC to prosperity.

He was one of Burke's first hires, in early 2011, when Comcast took control of NBCUniversal from General Electric Co. Greenblatt was previously a TV producer (Six Feet Under) and had a successful run as Showtime's top programming executive, introducing such shows as Weeds and The Tudors.

In an interview, Greenblatt said his decision to leave NBC was "a long time in coming … but I kept talking myself out of it." A year ago, Greenblatt extended his deal to remain chairman of NBC Entertainment.

"It is a great gig, things are going well with the company, and I have amazing bosses," Greenblatt said. "But I was starting to feel that I did all that I could do here and that I needed a new challenge."

Greenblatt, 58, said he hasn't figured out his next venture. He has been involved in producing a theatrical version of Tootsie, which is scheduled to premiere on Broadway next spring after its Chicago run.

"We will see what the town has to offer," he said, adding that he will assist Cheeks and Telegdy as needed. "I think it will be a seamless transition."