It's been 20 years and 3,901 episodes since "Late Show with David Letterman" premiered on CBS in 1993. To celebrate the milestone on Thursday, Letterman invited his very first guest, Bill Murray, whom he praised as "the gold standard in American comedy," back to the show. 

"Every film would be better if Bill was in it," the host said. Murray spent the next 15 minutes or so demonstrating why this was not mere hyperbole. Dressed as Liberace, he entered the stage via a white limousine. 

"I go over the top sometimes," Murray said. Case in point, a billboard he bought, theoretically as an anniversary gift for Letterman but featuring a giant portrait of himself. 

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There was a touch of the usual promotional banter sprinkled throughout their lengthy conversation, with Murray plugging his new project, the George Clooney-directed "The Monuments Men" ("It's a meatloaf of a film. It's got everything.") 

But mostly Murray was there to ham it up, such as when he retrieved a "time capsule" he'd buried beneath the stage at the Ed Sullivan Theater during his first appearance on "Late Show." (Its contents: A copy of the New York Post with a front-page story about Jay Leno and one of Dave's old toupees.)

Then Murray capped it off with a brief, mellifluous performance of  the No. 1 song of 1993, "I Will Always Love You."

Brings tears to the eyes, doesn't it? 

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