David Letterman's Most Important Moments Didn't Bring Laughter

David Letterman leaves a legacy that extends far beyond comedy.

On May 20th, David Letterman will end his legendary 34-year career in television making people laugh with stupid pet tricks and Top 10 lists.

Read: David Letterman Says Age Was a Factor in Leaving 'Late Show' 

But some of Letterman's most memorable moments have nothing to do with laughter.

On his first show following the terrorist attacks on September 11, 2001, he took to the airwaves and said, “This is going to be tough. It is terribly sad, it is terribly sad.”

Former CBS anchorman Dan Rather was his guest that night.

He told INSIDE EDITION, “They asked me if I would be on the show and I did not hesitate.”

Rather lost his composure and had to be comforted by Letterman.

Letterman replied, “You are a professional but good Christ, you are a human being." 

Rather explained to INSIDE EDITION, “I thought that night he was magnificent. He understood what was happening. He understood that the moment had suddenly consumed me when I tried to say those lines from 'America, the Beautiful.'" 

Read: David Letterman Welcomes Stephen Colbert

Letterman's own emotions boiled over after he had quintuple bypass surgery. He brought his entire medical team on the air to thank them.

He said then, "It was five weeks ago today that these men and women saved my life." 

As fans of the Late Show know, Letterman is a softie at heart and loves tradition.

Every year he brings bird callers on stage and there's his annual love fest with singer Darlene Love. She has performed her Christmas hit "Baby, Please Come Home," on the show every holiday season for 29 years straight years.

Love told INSIDE EDITION, "It was going to be special to a lot of people around the country. You know, people would walk up to me and tell me the phrase that David Letterman started, 'Christmas is not Christmas until I hear Darlene Love sing this song.'"

Last December, Letterman pulled out all the stops as she sang the talk show host's favorite Christmas song for the last time.

CBS’ 90-minute special, David Letterman: A Life on Television, will air tonight at 9:30.

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