Dick Ebersol, who had defined NBC’s formidable Olympic presence since the mid-1990s and who was the last of the high-profile TV sports impresarios, resigned abruptly on Thursday after negotiations on a four-year contract collapsed.

Mr. Ebersol, 63, has had a colorful television career in everything from sports to comedy, and a personal life marked by the death of a young son and his own near-death in a plane crash.

But he has been best known for his work with the Olympics, and his departure could significantly change what is expected to be a vigorous battle for the television rights for the next two Games. On June 6, he was to lead a contingent of executives from NBC and its parent company, Comcast, to Lausanne, Switzerland, for an auction for the 2014 and 2016 Olympics. He will not be making that trip.

“If I wasn’t going to produce them,” he said Thursday, “I wasn’t going to be part of the process.”

This will be Comcast’s first Olympic bid since the company took over NBC Universal earlier this year.