Tonight, after 33 years in late night television, David Letterman will preside over his final episode of the "Late Show."
Letterman leaves behind a very different late-night landscape than the one he helped pioneer, starting in 1982 when he first followed Johnny Carson's "Tonight" show with "Late Night with David Letterman," before moving in 1993 to CBS's the "Late Show, where he went head-to-head against Carson's successor Jay Leno.
Now it's hard to imagine late night without him. So much of what we think about late-night television is in no small part because of Letterman.
Here now is our Top 10 list of how David Letterman changed late-night TV.
10. Before Letterman, late night was synonymous with one person: Johnny Carson.
Letterman has outlasted even his mentor, the late Johnny Carson, who signed off from late night after three decades.
Carson created the blueprint of late-night -- monologue, band, witty banter with celebrity guests and occasional comic bits. But Letterman immediately set out to do something different.
"A lot of what we did was dictated by Carson," he told the New York Times recently. "There were so many restrictions. So that was the framework we were handed, which was fine, because then they gave us an excuse not to think of that thing to do."
9. He wasn't afraid to experiment.
That meant not being afraid to throw something against the wall and see if it would stick, and sometimes it did.
"I never knew if the stupider things we did or the more traditional things we did would work," Letterman told the Times. "I didn’t know if the stupid stuff would alienate people. I didn’t know if the traditional stuff would be more appealing. And then, when I look back on it now, of course the answer is, you want to do the weird thing."
8. He made oddballs and ordinary people the stars.
Long before Jimmy Kimmel pulled his first prank or made security guard Guillermo Rodriguez a star, Letterman carved a home for oddballs like Andy Kaufman, whose slap fight with wrestler Jerry Lawler is legendary, or Larry "Bud" Melman, the "Late Show" mascot who was given wacky chores like handing out hot towels at New York's Port Authority bus terminal, or Chris Elliott, who lived under the seats on the "Late Show" set.
He even made his mom, Dorothy Marie Mengering, famous by having her report from the 1994 winter Olympics.
7. He gave us stupid pet tricks.
Letterman didn't limit himself to two-legged guests, though. He brought over stupid pet tricks from his morning show, making it one of the most talked about segments of his show and a late night institution.
The segment was born out of necessity -- to fill airtime when Letterman earned his first late-night show on NBC -- but it caught fire with the audience and more than 130 segments have aired over Letterman's three shows.
6. He created the first-late night rivalry.
Long before the Jimmys (Kimmel and Fallon), there was Letterman and Leno, with fans and celebrities lining up to choose their favorites.
The war between Letterman and Leno was real -- and became the subject of endless articles, books and a TV movie. In the end, Leno won out, but Letterman gave him a run for his money.
"We prevailed for a while, and then I lost my way a little bit. Quite a little bit," Letterman explained to the New York Times. "And at that point, there was not much I could do about it. People just liked watching his show more than they liked watching my show."
5. He wasn't afraid to make a celebrity mad.
Letterman didn't take a shine to every celebrity guest, which made his fans love him more.
Similarly, some celebrities went out of their way to avoid him. But when they finally made an appearance on his show, it was always an event. Like when Cher, visiting for the first time, called him an a**hole. Or when Oprah Winfrey, after years of refusing to do his show following an appearance in 1989, finally made her second visit to the "Late Show" in 2005 -- an event Letterman dubbed "the Super Bowl of Love."
Winfrey and Letterman finally buried the hatchet last week, when he made an appearance on her "Oprah's Next Chapter" and she explained why it took her 16 years before she did his show again.
Letterman came to define the era of snark.
Chomping on his cigar, often impatient, sometimes downright bored by his guests, he made celebrities squirm long before the fake news hosts Jon Stewart and Stephen Colbert, who is taking over Letterman's late-night slot.
But to counter that, there was the goofy and vulnerable Letterman, who wasn't afraid to let his flaws show.
"I’m naked and afraid," he told Jane Pauley, describing his feelings about leaving late night after 33 years.
3. He showed the way to face a scandal, head on.
When news broke in 2009 that Letterman was the target of an extortion attempt stemming from sexual relationships he had with his female staffers, the late-night host faced the scandal head on.
At the top of his show on Oct. 5, Letterman told the audience, "I'm terribly sorry," adding that his wife, Regina Lasko, "has been horribly hurt by my behavior, and when something happens like that ... you try to fix it.... So let me tell you folks: I got my work cut out for me."
About his stunning public mea culpa, Letterman told the Times, "I didn’t know what else to do. I couldn’t think of a really good lie."
2. He built a production powerhouse.
Like Winfrey, Letterman knows his way around a boardroom just as well as his own set.
His production company, Worldwide Pants, not only produced the "Late Show" but was behind a number of TV shows, including "Everybody Loves Raymond" and "The Late, Late Show.
So even if Letterman won't be on TV screens every night, his influence will continue behind the scenes.
1. He gave us the Top 10 List.
Thanks to Letterman, there's a Top 10 list for just about everything -- including this story!
The list was the inspiration of several writers who were ridiculing the "eligible bachelor" list in a New York paper and thought they could put together "such nonsense" themselves.
The very first one, "The Top Ten Things That Almost Rhyme With Peas" was broadcast on Sept. 18, 1985.
The list moved with Letterman from NBC to CBS and became one of the highlights of the program, often with guest presenters such as Robert De Niro and Al Pacino, Casey Kasem and President Barack Obama, before he became president.