In January 2000, Letterman was rushed into emergency surgery for a quintuple bypass. When he returned on Feb. 21, 2000, it was like Letterman had been replaced with a new man. Not afraid to show his human side now, Letterman brought out the doctors and nurses who performed the surgery and saved his life. He thanked them profusely and sincerely.

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In the weeks after the terrorist attacks of Sept. 11, 2001, there was some discussion about how late-night comedians could go on in the face of such tragedy. The nation was shaken to its core and was thinking more about war than late-night jokes. The first late-night program to return to the air was "Late Show," which taped in the same city as the World Trade Center attack. Letterman's emotional opening on Sept. 19 was striking for a man not known for such displays. It set the tone for the rest of the late-night hosts on their subsequent returns.

Similar to his retirement announcement, Letterman shocked his studio audience on Oct. 1, 2009, when he told them that he'd been the victim of an extortion attempt because he'd had affairs with female members of his staff. The news soon centered on one staffer in particular, his personal assistant Stephanie Birkitt, whose boyfriend, "48 Hours" producer Robert J. Halderman, attempted to blackmail Letterman.

Birkitt was placed on "paid leave of absence" and Halderman served four months in jail. The affair landed Letterman's name in the tabloids and made his personal life, something Letterman had long guarded closely, something for open discussion.

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