FILE - In this Sept. 10, 1973, file photo, Muhammad Ali, right, winces as Ken Norton hits him with a left to the head during their re-match at the Forum in Inglewood, Calif. Norton, a former heavyweight champion, has died, his son said, Wednesday, Sept. 18, 2013. He was 70. (AP Photo/File)

Ken Norton, who in the course of 12 hard-fought rounds in 1973 was transformed from an unknown heavyweight into one of the most famous boxers in the world by virtue of a victory over Muhammad Ali, died Wednesday in a Las Vegas care facility. He was 70.

Norton was a thickly muscled ex-Marine who had little notoriety when he faced Ali on March 31, 1973, at the San Diego Sports Arena. But Norton broke Ali's jaw in the second round and went on to earn a split-decision victory that would define him as one of his era's greats.

The Seventies were a golden age for heavyweights, with legends such as Ali, Joe Frazier, George Foreman and Larry Holmes among many others competing at a high level, and Norton fit right in with that group.

Ali beat him in a hotly contested rematch later in 1973, and after the fight was singing Norton's praises.

"Norton is a better fighter than any other fighter I've fought, except maybe Joe Frazier," Ali said.

Gene Kilroy, Ali's former business manager, was a good friend of Norton's and visited him at the Veteran's Administration hospital in Las Vegas two weeks ago. He said Norton was unable to speak, but loved seeing the boxers that Kilroy brought to visit.

"He was a good guy and an outstanding fighter," Kilroy told Yahoo Sports. "I can tell you this: Ali had tremendous respect for him. He had that awkward style, where he'd shoot his jab up from the waist, and it was very unusual. Most guys throw the jab from the shoulder, and that always gave Ali trouble."

Norton was 42-7-1 with 33 knockouts and briefly held the WBC heavyweight title. He was awarded the WBC belt in 1978 when then champion Leon Spinks opted to face Ali in a rematch rather than defend it against Norton.

In his first defense, he lost the title to Larry Holmes in one of the greatest heavyweight title fights in history. The bout was dead even after 14 rounds and Holmes won a spectacular 15th on two of the three judges' cards to earn a split decision win and claim the belt.

Norton was elected to the International Boxing Hall of Fame in 1992, even though he never won a heavyweight title fight. In 1998, Ring Magazine editors tabbed him as the 22nd greatest heavyweight ever. Norton had quality wins over Ali, Jimmy Young and Jerry Quarry, among others.

"He was a truly a nice guy and he was a dedicated, brave, hard-working fighter," said Top Rank's Bob Arum, who promoted several of Norton's fights. "He struggled against guys who could really punch: Foreman, Earnie Shavers, [Gerry] Cooney, even a guy like Duane Bobick. But he was a tough out for anyone and when he was fighting someone who wasn't a massive fighter, he was right in the fight all the time."

Norton was also an actor and starred in the movie, "Mandingo," as well as several television shows. He is the father of former NFL linebacker Ken Norton Jr.

Norton, who built his reputation on his win over Ali, got a rubber match against "The Greatest," at Yankee Stadium in 1976 during a police strike in New York. It was a wild scene, and Ali won a hotly disputed decision to retain the WBA/WBC belts.

The fight with Holmes was his last hurrah. After that, he went 2-2-1 in his final five and retired after being knocked out by Cooney in the first round of a 1981 bout.