The cause was said to be heart failure, according to officials at Seoul National University Hospital, where Kim had been admitted since December 2011 for treatment of a type of thyroid disease. Kim had been under intensive care since March because of difficulty in breathing.
Kim "died early today after being treated at an intensive care unit since last March," a hospital official said on the condition of anonymity.
Police were on alert by mobilizing hundreds of riot police to the hospital and another Seoul hospital where a make-shift shrine for Kim was set up.
Kim was the boss of one of the three major criminal syndicates in the 1980s and gained fame for masterminding a brutal murder of a night club chief in 1986. He was sentenced to five years in prison, but his term was suspended after he was diagnosed with lung cancer.
But Kim was sentenced to 10 years in prison in 1992 on charges of setting up his criminal syndicate named "Beomseobangpa."
After Kim completed his sentence, he was mired in a serious of blackmailing and racketeering cases.