Arguably, Koch became even more popular after leaving City Hall. He hosted a radio show, wrote books, reviewed movies and even dispensed justice for a while on television's "The People's Court," succeeding Judge Marvin Wapner.
For years he teamed up with his close friend, former U.S. Sen. Alfonse D'Amato, R-N.Y., offering opinions and political analysis on the New York cable news station, NY1.
Koch also remained a political force. His endorsements were crucial in helping to elect two Republicans -- Giuliani as mayor of New York, in 1993, and George Pataki, as governor of New York, in 1994. And his backing of then-First Lady Hillary Rodham Clinton, a Democrat, eased the concerns of some older Jewish voters, helping her win a U.S. Senate seat in New York in 2000.
Edward I. Koch was born in the Bronx on Dec. 12, 1924 and reared in Newark, N.J. He served in the Army in World War II, landing in Cherbourg, France in September 1944 and earning two Battle Stars as a combat infantryman.
A graduate of the City College of New York and the New York University School of Law, Koch was a practicing attorney when he entered politics.
"I had no goals at that time, other than to meet people. Make friends," Koch told New York's Paper magazine. "I'm an achiever. I'm a good organizer, and I became a street spokesman for the Village Independent Democrats club. I was out every night on a soapbox."
Inspired by the speeches of presidential candidate Adlai Stevenson, Koch aligned himself with insurgents who opposed Tammany Hall, the long-running but decaying New York Democratic machine. Koch defeated the last Tammany boss, Carmine DeSapio, in a race for Democratic district leader in Greenwich Village in 1963.
The victory propelled Koch to the City Council, and then to Congress, where he served for nine years before winning a four-way Democratic primary for mayor in 1977 by shrewdly tacking to the political center – a shift that mirrored the political migration of white ethnic Democrats in the 1970s and '80s.
Koch cemented his popularity in 1980 when he acted as a kind of municipal cheerleader when a transit workers strike halted the subways and buses. Day after day, Koch stood on the Brooklyn Bridge, applauding New Yorkers walking to work.
"As I got on the bridge I began to yell, 'Walk over the bridge, walk over the bridge, we're not going to let these bastards bring us to our knees.' And people began to applaud. I knew I was onto something," he recalled in 2011.
During his administration, the go-go years on Wall Street in the 1980s led the city to new economic prosperity. He created a housing program which, over a ten year period, provided more than 150,000 units of affordable housing financed by city funds.
But Koch's brand of governing was not without dissenters. Koch had a troubled relationship with black voters. The relationship began its downward slide in 1978 with the death of a black businessman while he was in police custody. Other alleged cases of police brutality followed.
Racial unrest, his comments about Jesse Jackson, a municipal corruption scandal and soaring crime and homelessness doomed Koch's bid for an unprecedented fourth term.
Although Koch's endorsement helped Giuliani win 1993 mayoral race, the two had a falling out over what Koch saw as Giuliani's combative and authoritarian ways. Koch went on to write a book about it, "Giuliani: Nasty Man."
Koch also wrote "Citizen Koch; Ed Koch on Everything"; "I'm Not Done Yet: Remaining Relevant"; and "Eddie, Harold's Little Brother," a children's book that he co-authored with his sister, Pat Koch Thaler. He also teamed up with his good friend, John Cardinal O'Connor, who led the Archdiocese of New York, in writing, "His Eminence and Hizzoner," which traced Koch's shift to more centrist and conservative positions.
Koch will spend eternity in his beloved Manhattan. He announced in 2008 that he had purchased a plot at the Trinity Church cemetery, after learning that the church permits Jews to be buried there. It is the only active cemetery left in Manhattan.
"I don't want to leave Manhattan, even when I'm gone. This is my home," Koch explained. "The thought of having to go to New Jersey was so distressing to me."
The Associated Press contributed to this report.