David Letterman turns 75: a look back (17 images)

David Letterman interviews Howard Stern on "Late Show" on December 20, 1995. Photo by js/ Alan Singer/CBS/UPI

Talk show host David Letterman speaks to the media before the start of the Indianapolis 500 at the Indianapolis Motor Speedway on May 25, 2003. Photo by Mike Bryand/UPI

Letterman takes time during the race to sign some autographs in Indianapolis on May 29, 2005. Letterman is co-owner with Bobby Rahal of three cars for this year's Indianapolis 500. He paid tribute to Johnny Carson, an inspiration of his, after his death that year. Photo by Mike Bryand/UPI

Letterman watches his team prepare for the running of the Indianapolis 500 on May 28, 2006. That same year he said he had no intention of stepping down from the late show anytime soon, being age 58 at the time. Photo by Mike Bryand/UPI