Even in his 80s, Koch still exercised regularly and worked as a lawyer for the firm Bryan Cave.
At his 80th birthday bash, Bloomberg said Koch was "not only a great mayor and a great source of advice and support to other mayors, he happens to be one of the greatest leaders and politicians in the history of our city."
He had been in the hospital twice in 2012, for anemia in September and then for a respiratory infection in December. He returned twice in January 2013 with fluid buildup in his lungs.
He had undergone surgery in June 2009 to replace his aortic valve and gallbladder surgery a month later. He had a pacemaker inserted in 1991 and was hospitalized eight years later with a heart attack. In early 2001, he was hospitalized with pneumonia.
Koch was born in the Bronx on Dec. 12, 1924, the second of three children of Polish immigrants Louis and Joyce Koch. During the Depression the family lived in Newark, N.J.
The future mayor worked his way through school, checking hats, working behind a delicatessen counter and selling shoes. He attended City College and served as a combat infantryman in Europe during World War II, earning his sergeant stripes.
He received a law degree from New York University in 1948 and began practicing law in Manhattan's Greenwich Village neighborhood, where his political career began as a member of the Village Independent Democrats, a group of liberal reformers. He defeated powerful Democratic leader Carmine DeSapio, whose roots reached back to the corrupt Tammany Hall political machine, in a race for district leader.
Koch was elected to the City Council and then to Congress, serving from 1969-77 as representative for the "Silk Stocking" district that was then known for its millionaire Park Avenue constituency.
The liberal Koch was the first Democrat to represent the district in 31 years. But his politics edged to the center of the political spectrum during his years in Congress and pulled to the right on a number of issues after becoming mayor.