After leaving City Hall in January 1990, Koch battled assorted health problems and heart disease.
The larger-than-life Koch, who breezed through the streets of New York flashing his signature thumbs-up sign, won a national reputation with his feisty style. "How'm I doing?" was his trademark question to constituents, although the answer mattered little to Koch. The mayor always thought he was doing wonderfully.
Bald and bombastic, paunchy and pretentious, the city's 105th mayor was quick with a friendly quip and equally fast with a cutting remark for his political enemies.
"You punch me, I punch back," Koch once memorably observed. "I do not believe it's good for one's self-respect to be a punching bag."
The mayor dismissed his critics as "wackos," waged verbal war with developer Donald Trump ("piggy") and mayoral successor Rudolph Giuliani ("nasty man"), lambasted the Rev. Jesse Jackson, and once reduced the head of the City Council to tears.
"I'm not the type to get ulcers," he wrote in "Mayor," his autobiography. "I give them."
When President George W. Bush ran for re-election in 2004, Koch, a Democrat, crossed party lines to support him and spoke at the GOP convention. He also endorsed Mayor Michael Bloomberg's re-election efforts at a time when Bloomberg was a Republican. Koch described himself as "a liberal with sanity."
He was also an outspoken supporter of Israel, willing to criticize anyone, including President Barack Obama, over decisions Koch thought could indicate any wavering of support for that nation.
In a WLIW television program "The Jews of New York," Koch spoke of his attachment to his faith.
"Jews have always thought that having someone elevated with his head above the grass was not good for the Jews. I never felt that way," he said. "I believe that you have to stand up."
Under his watch from 1978-89, the city climbed out of near-financial ruin thanks to Koch's tough fiscal policies and razor-sharp budget cuts, and subway service improved enormously. But homelessness and AIDS soared through the 1980s, and critics charged that City Hall's responses were too little, too late.
Koch said in a 2009 interview with The New York Times that he had few regrets about his time in office but still felt guilt over a decision he made as mayor to close Sydenham Hospital in Harlem. The move saved $9 million, but Koch said in 2009 that it was wrong "because black doctors couldn't get into other hospitals" at the time.
"That was uncaring of me," he said. "They helped elect me, and then in my zeal to do the right thing, I did something now that I regret."
Among his favorite moments as mayor was the day in 1980 when, seized by inspiration, he walked down to the Brooklyn Bridge during a rare transit strike and began yelling encouragement to commuters walking to work.