Carlos De Leon, who won the WBC cruiserweight world title four times, died on Wednesday, New Year's Day, in Buffalo, New York. He was 60.
The WBC announced his death, but the cause had not been determined.
"The WBC family is sad to report the sudden passing away of one of the greatest cruiserweight champions, Carlos De Leon," WBC president Mauricio Sulaiman announced. "We join his family in grief. May he rest in peace."
De Leon (53-8-1, 33 KOs), who was born in Puerto Rico and known as "Sugar" throughout his 1974 to 1990 professional career, was the first two-time cruiserweight world titlist and faced several well known opponents during his 21-year career, including Evander Holyfield, Corrie Sanders, Johnny Nelson, Brian Nielsen, Leon Spinks, Marvin Camel and Yaqui Lopez.
In 1980, fighting at the Superdome in New Orleans on the undercard of the famed "No Mas" welterweight world championship rematch between Sugar Ray Leonard and Roberto Duran, De Leon won a 15-round majority decision over Camel to take his cruiserweight world title when the division, which had been created in 1979, used a 190-pound limit. Years later the limit was increased to 200 pounds.
Two fights later, De Leon would knock out Camel in the eighth round of a rematch before losing the belt to ST Gordon by second-round knockout in 1982. De Leon rebounded to win two fights in a row, including a sixth-round knockout of former heavyweight world champion Spinks, before he turned the tables on Gordon and regained the title by unanimous decision.
De Leon made three successful defenses, including by fourth-round knockout of Lopez, before dropping a split decision to Alfonzo Ratliff that cost him the belt in 1985.
After Ratliff quickly lost the title to Bernard Benton, De Leon regained the belt by beating Benton by majority decision in 1986.
De Leon made three successful defenses in that title reign before squaring off with Holyfield, who owned the two other major belts in the division, for the undisputed cruiserweight world title in April 1988. Holyfield stopped De Leon in the eighth round to become the first undisputed champion in division history.
Holyfield then vacated the titles and moved up to heavyweight, which gave De Leon a chance to fight for the WBC vacant belt in his next fight, and he knocked out Sammy Renson in the ninth round in 1989.
Following a draw with Nelson, who would go on to win a world title and make a division-record 13 title defenses, De Leon lost his belt by 11th-round disqualification -- for hitting after the bell -- to Massimiliano Duran in July 1990 in what turned out to be De Leon's 16th and final world title bout. De Leon finished his career 11-4-1 in world title bouts.
A two-year layoff followed, and when De Leon returned he did so as a small heavyweight and won eight low-level fights in a row before suffering knockout losses in his final two bouts against Sanders in the first round in 1994 and Nielsen in the third round in 1995.
De Leon's son, Carlos De Leon Jr. (22-3-2, 14 KOs), boxed professionally from 2001 to 2015.