David Letterman

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In this photo provided by CBS, talk show host Keith Olbermann, left, chats with host David Letterman on the set of the “Late Show with David Letterman,” Tuesday April 3, 2012 in New York. (AP Photo/CBS, Jeffrey R. Staab)

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In this photo provided by CBS, Sirius radio personality Howard Stern throws money to the audience on the set of the ìLate Show with David Letterman,î Wednesday, Feb. 1, 2012 in New York. The money was set aside by Letterman to entice actor Brad Pitt to appear on the show. (AP Photo/CBS, John Paul Filo)

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In this photo released by CBS, host David Letterman, right, and comic Jay Thomas get ready to throw footballs at the Late Show Christmas tree during the annual Late Show Holiday Quarterback Challenge on the set of "Late Show with David Letterman," airing Thursday, Dec. 23, 2011 on the CBS Television Network. Thomas and Letterman each take turns tossing footballs at the Late Show Christmas tree to try and knock off the giant meatball perched at its top. (AP Photo/CBS, John Paul Filo)

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Texas Gov. Rick Perry reads the "Top Ten" list on David Letterman's Thursday show. He was a late addition to the show after stumbling in Wednesday's GOP debate. (CBS via Associated Press)

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In light of a recent threat on a jihadist website against David Letterman, actor Ashton Kutcher wore a bulletproof vest and a helmet to a taping of the host's late-night talk show Wednesday. (CBS via Associated Press)

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David Letterman

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** FILE ** In this April 21, 2010 file photo released by CBS, host David Letterman is shown on the set of the "Late Show with David Letterman," in New York. Letterman is back at "Late Show" Monday, Aug. 22, 2011, after a two-week vacation, his first day at work since a threat against his life was posted on a website. Last week, a frequent contributor to a jihadist website urged Muslim followers to "cut the tongue" of the late-night host because of a joke Letterman had made about al Qaeda leaders. (AP Photo/CBS, Heather Wines)

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The lobby of the Ed Sullivan Theater, where David Letterman tapes his "Late Show," was trashed by a struggling actor on Sunday, according to New York police. "The inside looked like it was a drunken bar brawl," an police source said. (Associated Press)

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Osama bin Laden was the focus of many a late-night talk-show quip Monday, as (clockwise from top left) Jay Leno, David Letterman (with guest Brian Williams), Jimmy Fallon and Jon Stewart all made light of the al Qaeda leader's death.

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FILE - In this July 7, 2009 file photo, actor Sacha Baron Cohen dressed as his character Bruno leaves a taping of "The Late Show with David Letterman" in New York. (AP Photo/Charles Sykes, file)

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In this photo released by CBS, New York City Mayor Michael Bloomberg, left, shares a laugh with host David Letterman on the set of the "Late Show with David Letterman," in New York, Wednesday, Sept. 29, 2010. (AP Photo/CBS, John Paul Filo)

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** FILE ** In this Feb. 11, 2009, file photo, actor Joaquin Phoenix arrives for a taping of "The Late Show with David Letterman" in New York. (AP Photo/Charles Sykes, File)

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In this publicity image released by ABC, talk show host David letterman, third left, joins from Left, Whoopi Goldberg, Barbara Walters, Joy Behar, Sherri Shepherd and Elizabeth Hasselbeck, co-hosts of the daytime talk show, "The View," Tuesday, Sept. 7, 2010 in New York. (AP Photo/ABC, Heidi Gutman)

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In this photo released by CBS, U.S. World Cup soccer team midfielder Landon Donovan, left, talks with host David Letterman on the set of the "Late Show with David Letterman," Tuesday, June 29, 2010, in New York. (AP Photo/CBS, Heather Wines)

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ASSOCIATED PRESS In this photo released by CBS, U.S. World Cup soccer team midfielder Landon Donovan, left, talks with host David Letterman on the set of the "Late Show with David Letterman," Tuesday, June 29, 2010, in New York. Donovan, a key player for Major League Soccer's Los Angeles Galaxy, scored three of the U.S. team's five goals in 2010 World Cup, including a last-minute score against Algeria that sent the team into the second round of tournament play.

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** FILE ** David Letterman admits during an October 2009 broadcast of "The Late Show" to having been sexually involved with some female employees. (AP Photo/CBS)

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Late-night talk-show host David Letterman is seen as an "agent of influence" in Saudi Arabia, according to one of the diplomatic cables leaked by WikiLeaks.