• by Wayne Friedman , September 15, 2015

Nina Tassler, CBS’s longtime entertainment chief, is leaving the network after nearly 20 years.

Overseeing all TV programming/production areas, Tassler -- chairman of CBS Entertainment, presided over CBS’ steady prime-time programming lineup for nearly two decades, earning the network No. 1 status among all prime-time viewers, according to Nielsen, for 12 of the last 13 years.

She had been at the top entertainment post at the network for 11 years and 18 years overall at the company -- responsible for a number of top shows, including “The Big Bang Theory,” “The Good Wife” and “How I Met Your Mother.” As a CBS development executive, she oversaw franchise shows like “CSI” and “NCIS.”

Another longtime veteran -- Glenn Geller, who has been with CBS for 14 years, most recently as EVP, current programming for CBS Entertainment and CBS Television Studios -- will now become president of CBS Entertainment.

Geller will be responsible for prime time, daytime and late night, as well as program development in all genres, including comedy, drama, reality, specials and long-form programming.

Although CBS wasn’t always No. 1 in key 18-49 viewers, media-buying executives credit the network with steady and predictable results -- something longtime TV marketers place in high regard.

Tassler previously worked as a senior TV executive at Warner Bros. Les Moonves, president/chief executive officer of CBS Corp., was also a veteran at Warner Bros. Moonves came to CBS in 1995; Tassler came over in 1997.

Tassler started as vice president of drama for CBS Productions, before moving to the network as SVP of drama development in 1998. She became president of CBS entertainment in 2004.

Tassler has expressed a desire to pursue theater and publishing projects, according to reports. She will continue in an advisory role with the company through at least 2017.