The long reign of Stupid Human Tricks and Top Ten Lists will come to an end next year, David Letterman said Thursday, in a surprise announcement that signaled not just his retirement but also a potential generational change in late-night television.

“I’m retiring,” Letterman told his studio audience Thursday afternoon at the New York taping of “Late Show.” The news, delivered by Letterman from behind his desk, seemed to momentarily stun the Ed Sullivan Theater audience members, who, after a beat, gave him a standing ovation.

A brilliant absurdist comic who has been a fixture on network television for most of the past 34 years — a longer period even than his comedy hero, Johnny Carson — Letterman betrayed little emotion beyond a smile in disclosing the news. He gave no date for his depature, except to say that it would be next year, when his current contract ends.

Letterman’s decision to end his 21-year run on CBS follows the recent retirement of Jay Leno from “The Tonight Show” in February, meaning that next year, the turnover on the two franchise late-night shows will be complete. A generation ago, in the early 1990s, the two men competed intensely to replace Carson as host of “Tonight.” Leno won the prize to succeed late-night TV’s father figure, but there was room for both. Letterman left NBC and created his own legacy on CBS via “Late Show,” a one-hour showcase of the Indiana-born comic’s arch irony and idiosyncratic style.

Letterman’s news, coming just shy of his 67th birthday Saturday, set off a flurry of speculation about who among the next generation of late-night comics might replace him.

The obvious names: the quirky Craig Ferguson, whom Letterman hired to follow him on CBS; Conan O’Brien, Leno’s onetime heir, now ensconced on TBS; the recent Oscars host Ellen DeGeneres; Comedy Central’s news parodists, Jon Stewart and Stephen Colbert; the acerbic Bill Maher from HBO; and Chelsea Handler, the stand-up comic and best-selling author who has hosted a talk show on the E! cable network.

Some even suggested Leno for the job — which, given his occasionally embittered relationship with Letterman, could be the kind of unexpected twist that Letterman might appreciate. The NBC host left ”The Tonight Show” while still atop the ratings, a position he maintained during most of his long rivalry with Letterman. Leno has been a strong draw among the older viewers CBS has traditionally attracted.

Letterman faces intense competition, and might be fading among a younger generation of viewers. Since his debut in February, Leno’s replacement, Jimmy Fallon, has attracted a nightly audience of about 5 million, roughly twice that of Letterman. In turn, Letterman maintains a small advantage over another younger rival, ABC’s Jimmy Kimmel, though Kimmel attracts more of the younger viewers whom advertisers pay a premium to reach.

CBS wasn’t talking about Letterman’s replacement Thursday. Instead, the network’s chief executive, Leslie Moonves, said in a statement: “When Dave decided on a one-year extension for his most recent contract, we knew this day was getting closer, but that doesn’t make the moment any less poignant for us. . . . Dave has given television audiences thousands of hours of comedic entertainment, the sharpest interviews in late night, and brilliant moments of candor and perspective around national events. . . .There is only one David Letterman.”

Letterman has given no hint of his post-“Late Show” plans. He is among the wealthiest of TV stars — not only as a result of his program, but also via his ownership of his production company, Worldwide Pants, which produces his show and Ferguson’s, among other programs. Among the company’s greatest hits has been the sitcom “Everybody Loves Raymond,” which aired on CBS from 1996 to 2005 and which has had a lucrative run in syndication.

In interviews, Letterman has repeatedly portrayed himself as a man who lives to be on television. “Forget everything but the hour of the show,” he told The Washington Post before receiving the Kennedy Center Honors from President Obama in 2012. “That’s just it. I don’t like anything — well, I endure every other aspect of the day. But the part of it I enjoy potentially is the hour of the show.”

A former weather forecaster and studio announcer, Letterman left Indiana in the 1970s to hone his stand-up act in Los Angeles.

In 1980, NBC gave him a live daily show that aired at 10 a.m. — a daring experiment for a time period that was dominated by game shows and soap operas.

Letterman’s embrace of absurdist stunts — such as wrapping himself in Velcro and bouncing off a trampoline onto an adherent wall — proved too extreme for the hour and the era. But NBC stuck with him, giving him the 1 a.m. slot after Carson’s 90-minute “Tonight Show” in 1982.

In addition to such standing features as Stupid Pet Tricks (and its human version), Letterman’s loony, almost non sequitur-like stunts became his signature. Many were inspired, at least in their absurdity and daring, bits, by Steve Allen’s antics as the first “Tonight” host in the 1950s. Among others, there was “Will It Float?” which was nothing more than a discussion between Letterman and his perpetual bandleader/sidekick Paul Shaffer about whether some object would sink in a huge vat of liquid, followed by a demonstration.

Letterman’s anarchic instincts might have endeared him most to younger viewers. Among his most famous moments was a 1985 bit in which he heckled the then-hosts of the “Today” show, Bryant Gumbel and Jane Pauley, via a bullhorn from a window high above them as they taped a segment on the Rockefeller Center plaza below. “I’m not wearing pants,” he announced.

In his interview with The Post in 2012, however, Letterman signaled that he was not far from the end of his TV career.

“I feel like I’ve tried everything I wanna try,” he said. “And I think to see a 65-year-old guy dunked in a suit of Alka-Seltzer into a tank of water — I think you’d worry about the man. . . . I’ll miss it. Sure, I’ll miss it. I’ll find something else to do.”


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