Richard Plepler, pictured in November 2017, stepped down from his post as HBO's chairman and chief executive. (Christopher Goodney/Bloomberg News)

Richard Plepler, one of the most influential people in Hollywood, announced Thursday afternoon that he would be resigning from his position as chairman and chief executive of HBO. The unexpected news arrives almost three decades into Plepler’s storied career at the cable network.

“In the past weeks, I’ve thought a lot about the incredible journey of this company in the nearly 28 years that I have been blessed to be here,” Plepler wrote in a memo to HBO employees. “It’s a journey of great pride and accomplishment because so many of you, and many others before us, have made HBO a cultural and business phenomenon.”

Plepler’s exit comes eight months after AT&T finalized its $85.4 billion acquisition of HBO’s parent company, Time Warner, forming WarnerMedia. Reports stated earlier this week that WarnerMedia was considering former NBC chairman Bob Greenblatt for a high-level executive position overseeing both HBO and Turner.

“Richard is one of the most successful executives in our industry and I have been fortunate to have his support over the last months,” WarnerMedia chief John Stankey said in a statement. “His vision, energy and passion helped to elevate HBO’s brand to what it has become today. Richard’s impact to our business and on the passionate viewers of HBO’s enduring programming will continue to be felt for years.”

Plepler had long been regarded as the face of HBO, having worked at the company since 1992. He rose in the ranks amid the success of series such as “The Sopranos,” “Sex and the City” and “Curb Your Enthusiasm” and was named co-president alongside Michael Lombardo in 2007, four years before “Game of Thrones” premiered. In 2013, Plepler became chairman and CEO.

HBO became the premier source of what is known as prestige television during Plepler’s time at the company. In his six-year tenure as CEO, according to a spokesman, revenue grew by roughly $2 billion, or by 40 percent. The cable giant also earned 165 Emmy Awards and 657 nominations in that time, and Plepler greenlit shows such as “Westworld,” “Boardwalk Empire,” “Big Little Lies,” “Girls,” “Veep” and “Last Week Tonight with John Oliver.”

“My dad always gave the best advice,” Plepler wrote in the memo. “Whenever there was a difficult decision to make, he counseled that since no one could ever have perfect visibility into the future, the best thing you could do was trust your instincts. It has been a touchstone for me throughout my life, and I have found myself returning to it again recently as I think about what is an inflection point in the life of this wonderful company. Hard as it is to think about leaving the company I love, and the people I love in it, it is the right time for me to do so.”