David Letterman's celebrated broadcast career

David Letterman began his television career in 1970 in his home town of Indianapolis as an anchor and weatherman on television station WLWI, now called WTHR. He received attention for his often unpredictable on-air behavior.

Letterman's 1978 headshot for Mary Tyler Moore's variety show, "Mary." The show lasted only 3 episodes.

Letterman guest hosted "The Tonight Show Starring Johnny Carson" on July 4, 1979. He became a favorite fill-in for Carson after making his first appearances as a guest in 1978.

Comedian Jay Leno chats with Letterman while he was guest hosting for Carson on July 4, 1979. The two became friends, then rivals, when Leno, not Letterman, replaced Carson in 1992.

David Letterman in NBC's Studio 6A on Jan. 19, 1982 after he made the announcement of his new NBC comedy show, "Late Night With David Letterman."

Letterman speaks with his first interview guest on "Late Night," actor and comedian Bill Murray, during the show's first taping on Feb. 1, 1982 in New York.

Letterman holds his Emmy award at the 37th Annual Primetime Emmy Awards ceremony in Pasadena, Calif, in 1985. Letterman's shows have garnered both critical and industry praise, receiving 67 Emmy Award nominations and winning 12 times.

David Letterman in his office at NBC on Jan. 28, 1986 after taping his show.

Madonna made her first appearance on "Late Night" with comedian Sandra Bernhard in 1988. Her first appearance on the show was a surprise addition to the celebration of the series’ 1,000th taping.

Letterman makes an appearance on "The Tonight Show" after Johnny Carson announced his retirement from the coveted late-night spot on Aug. 30, 1991.

The Ed Sullivan Theater in New York City became Letterman’s new home on Aug. 30, 1993 when he departed NBC and started "Late Show with David Letterman" on CBS.

Drew Barrymore turns to the audience after flashing Letterman on his birthday during the April 12, 1995 taping of the "Late Show."

Oprah Winfrey returned to chat with Letterman, 16 years after her previous visit, on Dec. 1, 2005. Following the interview, Letterman escorted Winfrey across 53rd street to the opening of her new Broadway show "The Color Purple."

Actor Joaquin Phoenix made a now infamous appearance on "Late Night" on Feb. 11, 2009 during an awkward chat announcing his retirement from acting and the beginning of his rap career. "What can you tell us about your days with the Unabomber?" Letterman teased the bizarrely bearded actor.

Letterman laughs during another edition of Stupid Pet Tricks on Feb. 24, 2011. It was one of many popular segments his show made famous.

President Barack Obama watches as Letterman, a 2012 Kennedy Center Honors recipient, kisses the hand of Russian prima ballerina Natalia Makarova during a reception hosted by Obama and first lady Michelle Obama for the honorees in the East Room of the White House in Washington on Dec. 2, 2012. On the right is actor Dustin Hoffman.

Nearly 32 years after his appearance as Letterman’s first interview on "Late Night," Bill Murray makes a surprise appearance alongside Lady Gaga on April 2, 2014, a day before Letterman announced his retirement.

Letterman, the longest-serving late-night talk show host in TV history, announced his retirement on April 3, 2014 during the taping of "Late Show". The final show airs at 11:35 p.m. Eastern on May 20.

Letterman's last few weeks have been warmly nostalgic, with Letterman entertaining old friends like Bill Murray, Tom Hanks, George Clooney. Actress Julia Roberts made her final visit to the Late Show with David Letterman, May 13.

David Letterman hosts his final broadcast of the Late Show with David Letterman May 20.