Former undisputed world middleweight champion Marvelous Marvin Hagler has died at the age of 66, his wife announced on Saturday.
Hagler had ruled the division from 1979, but was dethroned following a controversial defeat by Sugar Ray Leonard in April 1987.
Kay Hagler wrote on the official Marvelous Marvin Hagler Fan Club Facebook page: "I am sorry to make a very sad announcement. Today unfortunately my beloved husband Marvelous Marvin passed away unexpectedly at his home here in New Hampshire."
New Jersey southpaw Hagler was only knocked down once during his professional career and defended his middleweight crown 12 times.
In September 1980, Hagler fought Alan Minter at Wembley Stadium, winning by a stoppage in the third round after the British boxer was badly cut to claim his first world title.
During 1985, Hagler took on Thomas 'Hitman' Hearns at Caesars Palace, Las Vegas, which he won in three brutal rounds of a contest which became known as "The War".
Hagler took on Leonard in April 1987, a boxer who had retired twice and not fought for almost three years.
Leonard took victory on a split decision, and then retired immediately again afterwards, with Hagler denied a rematch.
Hagler retired from boxing in June 1988, with a record of 62 wins, two draws and three defeats.
Promoter Frank Warren said on Twitter: "Boxing lost an all time great today."
Former WBA and lineal featherweight world champion Barry McGuigan said on Twitter: "Shocked and deeply saddened to hear of the passing of the incredible Marvellous Marvin Hagler.
"I'm honoured to have spent some amazing times with him. My heartfelt sympathies to his wife Kay and his family. Rest in Peace Champ."