David Letterman was on his way up the network food chain in 1980. After being a guest on The Tonight Show starring Johnny Carson several times and even guest hosting the show on several occassions, NBC knew that they had to get Dave his own show. The network had wanted to establish themselves in morning television for a while, so the network gave the comedian from Indiana a 90 minute morning talk show in June 1980. The David Letterman Show was on the air!

Ratings were bleak but steady in the beginning as the elderly and unemployed called into local affiliates to complain that their favorite syndicated soap operas and game shows had been replaced with the gap-toothed funnyman. As the ratings declined further NBC decided to throw in the towel and told Dave that his show would cease production in October.

With six weeks of airtime to fill and the fear of cancelation gone (since they'd already been canceled), Dave and his writing staff went a little crazy on the air and began filling time in any way they could think of. They held poodle races in the studio. They took the cameras down to the NBC cafeteria and interviewed whoever happened to be eating there. They flew in a farmer from Nebraska named Floyd Stiles and held a "Floyd Stiles Day". Even the now-popular Stupid Pet Tricks segment became a fixture of the show.

With the sudden burst of creativity and unheard of entertainment style now on the air the show became a modest hit in its closing days and even won two Emmy Awards. Nevertheless, in October 1980 the show went off the air and Dave was certain that his days in television were over.

However, NBC saw the ratings spike during the show's closing days and began to realize that the show played more like a late night talk show that aired in the morning. The network immediately signed Dave to a holding contract that would pay him $1 million if he was not given another show on the network in the near future. In 1981 Dave and the morning show crew moved to the 12:30am time slot and Late Night with David Letterman was born.


References:
The Late Shift book by Bill Carter