Patrick Tenore told the Los Angeles Times Norton died of congestive heart failure while undergoing rehabilitation from a stroke suffered last year.
Norton, coming in as a 5-1 underdog, shot to fame with a March 31, 1973, title decision over Muhammed Ali in San Diego during which he broke the champion's jaw.
But he fell to Ali in a rematch later that year at Inglewood, Calif., as well as in a 1976 decision at Yankee Stadium in New York.
Norton finished his boxing career with a record of 42-7-1 and 33 knockouts.
Son Ken Norton Jr. was an NFL linebacker for the Dallas Cowboys and San Francisco 49ers and is now on the coaching staff of the Seattle Seahawks.
Man spent 15 hours in jail for plugging electric car into an outlet at a school
Gal Gadot cast as Wonder Woman for 'Batman vs. Superman'