Replacing David Letterman at NBC seemed like a fool's errand. I despised Conan O'Brien for even trying.

On Thursday, that fool will retire from the talk show circuit after 28 years, leaving behind one of the zaniest, most memorable runs in TV history.

Truth is, I started warming up to the comedian even before he went on the air.

The morning that "Late Night With Conan O'Brien" premiered, the New York Times ran a column in which the guest writer tore apart a test show he had witnessed, ridiculing the new host for filling his monologue with knock-knock jokes, stealing his predecessor's Top Ten List and interviewing a guest who could eat oranges without getting juice on his shirt.

The piece was penned by O'Brien.

That self-deprecating wit would serve the newcomer well during the early seasons, as would edgy bits like Cute Animal Theater, in which puppies and kitties were dressed in white-hooded robes to re-enact a KKK rally.

The newcomer was smart enough to hire some of the most creative writers in the business, including Louis C.K., future "Better Call Saul" star Bob Odenkirk and Robert Smigel, who would give birth to Triumph the Insult Comic Dog, an NC-17 version of Don Rickles.

Then there was sidekick Andy Richter. I was so impressed with his chutzpah — he once slid down a muddy hill at Woodstock, then interviewed Melissa Etheridge while caked in dirt — that I spent a day with him in New York for a profile piece.

During that 1996 visit, I got to see that O'Brien could be even nuttier off camera. For the audience warmup, he bolted into a packed studio, climbed the stairs into the audience to gyrate wildly against a young female spectator while warbling "Burning Love."

A lot of that confidence melted into flop sweat during the celebrity interviews. For years, O'Brien seemed uncomfortable talking to anyone with a higher profile than Tony Randall.

But he improved. By the time he was tapped to take over "The Tonight Show" in 2009 from Jay Leno, he had grown into the role of a late-night elder.

During a visit to the KARE studios to promote the gig, he worked the room with ease, posing for more than 100 pictures with staffers and contest winners.

"I have no self-esteem," he said at the time. "I lost it years ago in a traffic accident."

His interactions with "ordinary folk" became his trademark. When NBC wanted to move his show to a later time slot so Leno could be brought back, O'Brien bolted. He moved in 2010 to TBS, where he did even more remote segments that showed off his ability to ad-lib while learning how to do the Irish jig or teaching the blues to kindergartners.

He may be the quickest wit since Groucho Marx.

But shortly after his jump to basic cable, I lost interest in O'Brien. There was too much action on the networks with newcomers Jimmy Fallon, Jimmy Kimmel and Stephen Colbert fighting for turf.

I came back a few years into the last presidential administration. While the Big Three were doubling down on Trump bashing, O'Brien was still focused on being goofy.

"If you come to us for the sharp political take, it's your fault," he said in 2020.

It was a welcome respite.

O'Brien, 58, isn't pulling a disappearing act. He's moving to HBO Max, where he'll continue to churn out episodes of his excellent docuseries, "Conan Without Borders," and occasionally produce variety specials.

But his daily dose of lunacy will be missed.

Thank you, Conan, for always acting the fool.