Mr. Koch's spokesman, George Arzt, said he died of congestive heart failure at 2 a.m. at NewYork-Presbyterian/Columbia hospital.

The former mayor 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.

Only his bouts of illness slowed Mr. Koch, most recently forcing him to miss the premiere on Tuesday of "Koch," a documentary biographical film that opened Friday in theaters nationwide.

Mayor Michael R. Bloomberg praised him as "an irrepressible icon, our most charismatic cheerleader and champion," calling him "a great mayor, a great man and a great friend."

Mr. Koch's 12-year mayoralty encompassed the fiscal austerity of the late 1970s and the racial conflicts and municipal corruption scandals of the 1980s, an era of almost continuous discord that found Mr. Koch caught in a maelstrom day after day.

But out among the people or facing a news media circus in the Blue Room at City Hall, he was a feisty, slippery egoist who could not be pinned down by questioners and who could outtalk anybody in the authentic voice of New York: as opinionated as a Flatbush cabby, as loud as the scrums on 42nd Street, as pugnacious as a West Side reform Democrat mother.

"I'm the sort of person who will never get ulcers," the mayor — eyebrows devilishly up, grinning wickedly at his own wit — enlightened the reporters at his $475 rent-controlled apartment in Greenwich Village on Inauguration Day in 1978. "Why? Because I say exactly what I think. I'm the sort of person who might give other people ulcers."

His political odyssey took him from independent-minded liberal to pragmatic conservative, from street-corner hustings with a little band of reform Democrats in Greenwich Village to the pinnacle of power as the city's 105th mayor from Jan. 1, 1978, to Dec. 31, 1989. Along the way, he put an end to the career of the Tammany boss Carmine G. De Sapio and served two years as a councilman and nine more in Congress representing, with distinction, the East Side of Manhattan.

With his trademark — "How'm I doin?" — Mr. Koch stood at subway entrances on countless mornings wringing the hands and votes of constituents, who elected him 21 times in 26 years, with only three defeats: a forgettable 1962 State Assembly race; a memorable 1982 primary in a race for governor won by Mario M. Cuomo; and a last Koch hurrah, a Democratic primary in 1989 won by David N. Dinkins, who would be his one-term successor.

Led New York Into Prosperity

In retrospect, how did he do?

By the usual standards of measuring a former mayor's legacy — the city he inherited, the challenges he faced, the resources available to meet those challenges and the extent to which his work endured beyond his term — historians and political experts generally give Mr. Koch mixed-to-good reviews.

Most important, he is credited with leading the city government back from near bankruptcy in the 1970s to prosperity in the 1980s. He also began one of the city's most ambitious housing programs, which continued after he left office and eventually built or rehabilitated more than 200,000 housing units, revitalizing once-forlorn neighborhoods.

Politically, Mr. Koch's move to the right of center was seen as a betrayal by some old liberal friends, but it gained him the middle class and three terms in City Hall. He was also the harbinger of a transformation in the way mayors are elected in New York, with candidates relying less on the old coalition of labor unions, minority leaders and Democratic clubhouses and more on heavy campaign spending and television to make direct appeals to a more independent-minded electorate.

In the end, however, he was overwhelmed by corruption scandals in his administration and by racial divisions that his critics contended he sometimes made worse.

This article has been revised to reflect the following correction:

Correction: February 1, 2013

An earlier version of this article misstated the number of candidates Mr. Koch faced in the Democratic primary for mayor in 1977. He faced six candidates, not seven.