Garry Shandling, the writer, actor, producer and comedian best known for his long-running and influential HBO series The Larry Sanders Show and his groundbreaking sitcom It’s Garry Shandling’s Show, died today at Cedars-Sinai Medical Center in Los Angeles. He was 66. No cause of death was released.

Shandling was born on November 29, 1949, in Chicago and raised in Tucson, AZ. He moved to Los Angeles in 1973, working in advertising before breaking into entertainment in 1975 with a script for Sanford and Son. During this period he wrote for Welcome Back, Kotter and was briefly involved with Three’s Company.

Shandling began doing stand-up comedy in 1978 after becoming frustrated with what he said was the “formulaic writing” common on situation comedies. He eventually caught the attention of The Tonight Show host Johnny Carson and made his first appearance on the program in 1981. He would go on to be a regular guest host until 1987.

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In 1986, he co-created It’s Garry Shandling’s Show with Alan Zweibel for Showtime. The groundbreaking series was a surreal, postmodernist parody of the sitcom genre starring Shandling as an exaggerated version of himself who knew that he was a character on a television show. Notable for breaking of the fourth wall, Shandling and his co-stars frequently interacted with the audience, called attention to the set and budgetary limitations and often made the audience part of episode storylines. The show also aired as part the Fox Television Network’s Sunday night lineup from 1988-90, introducing Shandling to a wider audience that laid the groundwork for his successful follow-up show.

That program was HBO’s The Larry Sanders Show, a satirical look at the world of late-night talk shows drawn loosely from his own experiences as guest host on The Tonight Show . Depicting late-night talk as a cesspool of ego, betrayal and unchecked ambition, the mock behind-the-scenes comedy featured Shandling as Sanders, along with Jeffrey Tambor as his sidekick “Hey Now” Hank Kingsley and Rip Torn as Arthur, the show’s producer. The series also was a launching pad for the careers of younger actor-comedians such as Janeane Garofalo, Wallace Langham, Bob Odenkirk, Mary Lynn Rajskub, and others. Jeremy Piven also was a regular for the first two seasons. During the show’s run, Shandling was approached by NBC to take over Late Night but declined, and The Larry Sanders Show later parodied the scramble to replace David Letterman.

Running for 89 episodes from 1992-98, The Larry Sanders Show instrumental in establishing HBO as a producer of original quality television programming and had enormous influence on TV comedy, particularly the deadpan, laugh-track-free tone and the frequent appearances by celebrities playing themselves. Nominated for 56 Primetime Emmy Awards, it won three (one for writing, one for directing and one for supporting actor for Torn). It also received numerous other accolades, including five CableACE Awards and a BAFTA. It ranked No. 20 on the WGA’s 2013 list of “101 Best Written TV Series.” WGA called it “a freshly acerbic glimpse into showbiz narcissism.”

Shandling was known to younger audiences for his appearances as Senator Stern in the Marvel films Iron Man 2 and Captain America: Winter Soldier. Other film roles include the Mr. Show film Run Ronnie Run, Zoolander, Dr. Dolittle and Over the Hedge. His final appearance in filmed entertainment was in a January episode of Jerry Seinfeld’s Comedians In Cars Getting Coffee entitled “It’s Great That Garry Shandling Is Still Alive.” On January 25, in one of his last public appearances, Shandling spoke at his old friend David Duchovny’s Hollywood Walk of Fame ceremony.

Shandling was well known in Hollywood for anonymously helping the careers of many now-prominent comedians and was an enormous influence on the likes of Judd Apatow, Ricky Gervais, Jon Stewart, Louis C.K., and Veep and The Thick of It creator Armando Iannucci. Like his old friend Carson, Shandling also was a generous humanitarian who anonymously gave financial support to many people directly affected by tragedies over the years. “Because of what he had gone through in his life, he knew truly what it was to be down, and he understood the spirit of kindness,” said Deadline’s Anita Busch, who was close friends with Shandling. “He was one of the most generous people I’ve ever known. He had a great perspective on what life is truly about.”

Shandling loved to box and co-owned his own ring in Santa Monica. Fittingly, he said during his Comedians in Cars Getting Coffee appearance: “What I want, at my funeral, is an actual boxing referee to do a count. And at 5, just wave it off and say, ‘He’s not getting up’.”

Shandling is survived by his cousin Michael.