Mr. Koch’s spokesman, George Arzt, said the former mayor died at 2 a.m. from congestive heart failure. He was being treated at NewYork-Presbyterian/Columbia hospital.

Mr. Koch had experienced coronary and other medical problems since leaving office in 1989. But he had been in relatively good health despite — or perhaps because of — his whirlwind life as a television judge, radio talk-show host, author, law partner, newspaper columnist, movie reviewer, professor, commercial pitchman and political gadfly.

Ebullient, flitting from broadcast studios to luncheon meetings and speaking engagements, popping up at show openings and news conferences, wherever the microphones were live and the cameras rolling, Mr. Koch, in his life after politics, seemed for all the world like the old campaigner, running flat out.