Ken Norton, who had three memorable fights with Muhammad Ali, breaking Ali’s jaw in winning their first bout, then losing twice, and who went on to become the World Boxing Council heavyweight champion, died Wednesday in the Las Vegas suburb of Henderson, Nev. He was 70.

His death was confirmed by his son Ken Jr., an assistant coach with the Seattle Seahawks of the N.F.L. and a pro linebacker for 13 seasons, The Associated Press said. Norton had been in poor health for several years after sustaining a series of strokes, The A.P. reported.

Norton defeated Ali on a 12-round split decision in 1973 to capture the North American Boxing Federation heavyweight title. Norton was an exceptionally muscular 6 feet 2 inches and 220 pounds, but he was a decided underdog in the first Ali fight.

“Ali thought it would be an easy fight,” Norton’s former manager, Gene Kilroy, was quoted by The A.P. as saying. “But Norton was unorthodox. Instead of jabbing from above like most fighters, he would put his hand down and jab up at Ali.”

Kilroy said that after the fight, Norton visited Ali at the hospital where he was getting his broken jaw wired, and Ali told him he never wanted to fight him again.

But the second bout in their trilogy came six months later, when Ali rallied to win a narrow split decision. In their final bout, Ali retained his World Boxing Council and World Boxing Association titles when he defeated Norton on a decision that was unanimous but booed by many in the crowd of more than 30,000 at Yankee Stadium in September 1976.

“I was never the same fighter after that,” Norton told Red Smith of The New York Times in October 1979. “I never trained so hard again, never could put the same feeling into it. I was at my best that night, in the best shape I ever was.”

In 1977, Norton knocked out the previously unbeaten Duane Bobick in the first round and defeated Jimmy Young in a 15-round split decision in a W.B.C. title elimination series. He became the mandatory challenger for the winner of the coming fight between Ali and Leon Spinks. Spinks defeated Ali for the championship but shunned Norton for his first defense in favor of a rematch with Ali. The W.B.C. stripped Spinks of the title and awarded it to Norton.

Norton made his first defense of the W.B.C. title in 1978 against Larry Holmes and lost by a 15-round split decision in one of boxing’s most exciting fights.

Kenneth Howard Norton was born Aug. 9, 1943, in Jacksonville, Ill., and starred in high school football, basketball and track. He attended Northeast Missouri State University (now Truman State University) on a football scholarship but was hampered by a shoulder injury in his first two seasons and enlisted in the Marine Corps. Norton started boxing while he was in the Marines, compiling an amateur record of 24-2 and winning the All-Marine Heavyweight Championship three times.

He turned pro in 1967 and won 16 straight bouts before being knocked out by Jose Luis Garcia. Soon afterward, he read Napoleon Hill’s motivational book “Think and Grow Rich.”

“I must have read that book 100 times while in training, and I became a stronger person for it,” the Web site BoxRec.com quoted him as saying. He said he believed in the book’s philosophy that a person could do the unexpected if he put his mind to it.

“So I train for my fights mentally as well as physically,” he said. “One thing I do is only watch films of the fights in which I’ve done well or in which my opponent has done poorly.”

Norton fought the undefeated George Foreman for the W.B.C. and W.B.A. heavyweight championships in 1974 and was knocked out in the second round. He stopped Jerry Quarry in five rounds in 1975 to regain the N.A.B.F. crown. In his next fight, Norton avenged his 1970 loss to Garcia with a fifth-round knockout.

After retiring for a time, Norton returned in 1980 and defeated the previously unbeaten Tex Cobb on a decision. The next year, Gerry Cooney, ranked No. 1 by the W.B.A. and the W.B.C., knocked Norton out in the first round in what became his final fight. Norton won 42 fights (33 by knockout), lost seven times and fought one draw.

Norton acted in several movies, most notably “Mandingo” (1975), in which he played the slave Mede, who is trained to fight by his owner.

Ken Norton Jr. played linebacker for the Dallas Cowboys from 1988 to 1993 and for the San Francisco 49ers from 1994 to 2000. He was a three-time Pro Bowl player with the 49ers.

In addition to Ken Jr., Norton’s survivors include his wife, Rose Conant; two other sons, Keith and Kenny John; and a daughter, Kenisha.