(Editor’s note: This story originally published at Boxing Junkie, part of the USA TODAY Network.)

Marvin Hagler, the Hall of Fame middleweight who dominated his era, has died, according to his wife, Kay. He was 66.

Kay Hagler broke the news on her husband’s Facebook fan 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,” her statement read. “Our family requests that you respect our privacy during this difficult time.”

She didn’t provide more details. According to TMZ, one of Hagler’s sons said his father was taken to a hospital after experiencing chest pains and trouble breathing at home. About four hours later, the family was notified that Hagler died.

Hagler, a superb boxer with knockout power and a granite chin, is considered one of the greatest boxers who ever lived.

“Marvelous” Marin Hagler, which became his legal name, was born in Newark, N.J., but moved with his family to Brockton, Mass., as a teen. He walked into the local gym of Pat and Goody Petronelli when he was 15 and never left.

He reportedly finished his amateur career with a record of 55-1 before turning pro in 1973. He fought his way to middleweight title contention by the late 1970s, with his first championship fight coming against WBA and WBC beltholder Vito Antuofermo in November 1979.

Hagler seemed to do enough to win the fight and the title but he had to settle for a split draw, which was widely criticized.

His breakthrough came in September 1980, when he destroyed Alan Minter – who had taken Antuofermo’s titles – in less than three full rounds to become the middleweight champion of the world.

That was the first step in one of the most dominating runs in the 160-pound division. Hagler held the title of undisputed champion for seven years, which included 12 successful defenses (11 of which came by knockout).

Among them was his classic brawl against Thomas Hearns in April 1985 at Caesars Palace in Las Vegas, which Hagler won by third-round knockout. The frenetic first round is considered one of the wildest in the history of boxing.

It was also the first fight in his “Four Kings” series with Hearns, Sugar Ray Leonard and Roberto Duran.

Hagler’s 13th defense came against Leonard, the 1976 Olympic gold medalist and former welterweight and junior middleweight titleholder, in April 1987 at Caesers.

The fight was competitive but Leonard, a significant underdog after a three-year hiatus from boxing, stunned the boxing world by winning a split decision to take the middleweight championship.

Two judges scored it for Leonard (118-110 and 115-113) and one of Hagler (115-113). The majority of those at ringside who were polled after the fight had Hagler winning.

In this August 1974 file photo, Marvin Hagler stands in the ring after his boxing bout against Sugar Ray Seales. (Peter Bregg, Associated Press)

Hagler always believed he deserved to win the decision.

“Even though the outcome wasn’t the way it should have been, publicly I still feel in my heart I won the Sugar Ray Leonard fight,” he said later.

Hagler, only 32 when he lost to Leonard, never fought again.

He was inducted into the International Boxing Hall of Fame in 1993. He became a regular and fan favorite at Hall of Fame weekend most years in Canastota, N.Y.

Hagler later became an actor and moved to Italy.