In this Feb. 1, 1982 file photo, Letterman, right, and guest Bill Murray appear at the taping of the debut of "Late Night with David Letterman" in New York.
"Late Night with David Letterman" host David Letterman, left, appears with host Johnny Carson during taping of "The Tonight Show," at the NBC Studio in Burbank, California, in this 1991 file photo. After 33 years in late night and 22 years hosting CBS' "Late Show," Letterman will retire on May 20.
Letterman makes a selfie with Oprah Winfrey during Oprah’s final appearance on the “Late Show with David Letterman."
Michelle Obama gives a “thumbs up” as host David Letterman watches on the set of the show on April 30.
President Barack Obama with host David Letterman talk during a break at a taping of CBS' "The Late Show with David Letterman" at the Ed Sullivan Theater in New York, May 4, 2015.
Former President Bill Clinton, left, makes his final appearance with Letterman on May 12.
Actor George Clooney, left, handcuffs himself to host David Letterman on the set of the “Late Show with David Letterman.”
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