CBS Entertainment Chairman Nina Tassler — a key architect of the network's success for more than a decade — is ending her run in charge of CBS programming at the end of the year, the company announced Tuesday.
Glenn Geller, who oversees CBS programming on the air, is being promoted to president of CBS Entertainment.
In his new role, effective immediately, Geller will oversee program development as well as prime-time, daytime and late-night programming.
The executive suite switch ends a long period of stability at CBS.
Tassler has been a trusted lieutenant of CBS Corp. Chief Executive Leslie Moonves for a quarter-century. The two worked together at Warner Bros. before Moonves recruited Tassler and several others to join him at CBS. Tassler also is the longest serving member of Moonves' original programming team.
"Nina and I have been colleagues and friends for 25 years," Moonves said in a statement. "We've enjoyed amazing success together, both here and at Warner Bros., and it's been a privilege to watch her talents and accomplishments grow."
CBS has been ranked as the No. 1 network in total viewers for 12 of the past 13 years. Tassler's talents — her eye for engaging material and strong relationships with producers and writers — have been instrumental in the network's success.
She has been in charge of CBS programming since 2004, when she stepped in the job of entertainment president.
Over the years, Tassler has helped nurture such hits as "The Big Bang Theory," "How I Met Your Mother," "CSI: Crime Scene Investigation," "NCIS," "The Good Wife," "Criminal Minds" and "Undercover Boss." She also was in charge of the transition in late night, helping recruit Stephen Colbert and James Corden.
Tassler joined CBS in 1997 as vice president of drama for CBS Productions.
She will continue in her current role as entertainment chairman until the end of the year, when she will segue into an advisory position that will run through at least 2017.
"I will always love this place, yet it is time for my next chapter, and I'm thrilled that I can pursue my other creative interests while still being part of the company," Tassler said in a statement.
Geller, meanwhile, has been part of CBS' executive team for 14 years.
For the past two years, he served as executive vice president for current programming. In that role, Geller oversaw creative issues and story lines for more than 30 prime-time shows on CBS and its sister network, CW.
Before joining CBS in 2001, Geller worked for three years in drama development at 20th Century Fox Television.
"When Nina told me her plans, we both knew we had an obvious successor in our own ranks," Moonves said. "Glenn brings outstanding skills to all parts of the creative and production process, and he has led large programming teams, both at the network and studio."