David Letterman is leaving a lasting legacy

There's longevity. There's stamina. And then, there's David Letterman, who, when he retires Wednesday, will have hosted 6,028 late-night talk-show broadcasts over 33 years.

Letterman, 68, was master of the acerbic interview: Probing entertainers and politicians alike, he was neither sycophantic, predictable nor encumbered by the late-night tradition of softball questions. Which is why, says frequent guest Olivia Wilde, "He doesn't seem to be working for a network."

After a decade on NBC's Late Night, he lost out to Jay Leno in the battle to replace Johnny Carson on the Tonight Show in 1992, and promptly bolted for CBS. Leno became the ratings victor, followed by his successor, Jimmy Fallon. But arguably it was Letterman who — with his combination of the absurd and the edgy — owned late night, if not in popularity then in cultural impact.

His departure comes at a turbulent time for late night, with Jon Stewart leaving the Daily Show in August, and Stephen Colbert taking over for Letterman in September.

"I look at the world as two guys: Johnny Carson and David Letterman. Those are the two guys who really set up what late night is," says CBS CEO Leslie Moonves. "David's influence was phenomenal. Whenever there was something important going on in America, you turned on David Letterman. He was the conscience of America, he was a bit of a social commentator, he was our local curmudgeon."

Before the now-ubiquitous celebrity viral videos, Letterman set the standard for late-night gab. He let Crispin Glover wallow in his agitated weirdness, and grilled Paris Hilton about her time behind bars, unfazed by her reluctance. "See, this is where you and I are different. This is all I want to talk about," he said, to applause. "Did you make any friends while you were in prison?"

Mostly, he wanted to know about other people, asking audience members about babies and professions, and asking celebrity guests about everything from hotel rooms (Cher) to body weight (President Obama).

"I've never met anyone who had the insatiable curiosity of David Letterman," says Late Show producer Robert Morton, whom Letterman fired in 1996. "It's the reason he was the best talk-show host ever."

But Letterman's few heartfelt moments are the best remembered, maybe because he shared so little of his private life with viewers. After 9/11, he wondered about the religious zealotry that caused the attacks, and pronounced New York the greatest city in the world. In 2003, he held up a photo of his newborn son Harry, stunned that he was a part of something so "beautiful." And he talked about his 2000 heart bypass surgery, parading his surgeons on stage.

"You can count on one hand the amount of people who can sustain decades of hosting late-night comedy. It's a very big deal. He has durability. Most people can't do this for decades," says Charles Grodin, who was both a guest, and a guest host.

Unlike other late-night hosts, Letterman didn't glad hand his guests backstage. Sometimes he'd briefly chat during commercial breaks, or he'd sway to the beats played by musical director and sidekick Paul Shaffer, or simply leave the set.

Which often left guests unprepared. "You have to be on your toes," says frequent guest and close friend Tom Brokaw. "He's very smart and very well read. He makes me think."

Contributing: Gary Levin