Former undisputed middleweight world champion 'Marvelous' Marvin Hagler has died at the age of 66, Ann.az reports citing BBC.
The American dominated the middleweight division from 1979 until his controversial defeat by Sugar Ray Leonard in April 1987.
"Today, unfortunately my beloved husband Marvelous Marvin passed away unexpectedly at his home here in New Hampshire," his wife Kay Hagler said.
Hagler took part in 67 fights during his 14-year professional career.
He won 62 of those, 52 by knockout, while he drew two and lost three times.
Hagler made 12 successful title defences and famously won the classic fight known as 'The War', when he beat Thomas 'Hit Man' Hearns in April 1985.
"Boxing lost an all-time great today," said boxing promoter Frank Warren.
Former world featherweight champion Barry McGuigan said he was "shocked and deeply saddened" to hear of the "incredible" Hagler's death.
The Irishman added: "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."
British heavyweight Derek Chisora said Hagler was "one of the greatest".