McCormack, who had historical ties to mobster Al Capone, and once was named the "Most Powerful Man in Sport" by Sports Illustrated, had been in a coma at a New York hospital since mid-January.
He founded the International Management Group, better known as IMG. Its stable of stars includes golfers Tiger Woods and Annika Sorenstam. Others include tennis stars Andre Agassi and Pete Sampras, football's Joe Montana and hockey's Wayne Gretzky.
"He was a genius when it came to sports marketing," Woods said. "If it wasn't for him, we wouldn't be in the position we're in now."
The story of McCormack's rise to the top of sports marketing is legendary.
It began with a handshake between McCormack and golf legend Arnold Palmer. He followed by signing golfers Gary Player and then-unknown Jack Nicklaus. Later, McCormack, a Yale law school graduate, branched out into other sports. He signed tennis great Rod Laver in 1968 and later Bjorn Borg, John McEnroe, Chris Evert and Martina Navratilova .
Eventually, McCormack's reach was felt in nearly every sport, and his decisions affected every top athlete.
"Mark has been both a friend and colleague for over 40 years, and has unquestionably been the catalyst in making golf the globally commercial success it is today," said PGA veteran Gary Player. "He was a visionary and a pioneer across all professional sports."
"The world of professional golf and sports generally lost a true leader today with the passing of Mark McCormack," said PGA Tour Commissioner Tim Finchem. "Mark was instrumental in the development of professional golf, not only in the United States, but throughout the world."
McCormack's corporation, based in Cleveland, employs more than 3,000 people and provides more than 5,000 hours of television programming for more than 200 countries.
It has has 80 offices in 32 countries. Under its umbrella, IMG is the largest independent producer of televised sports programming, top modeling agency, and biggest licensing agency in the world.
IMG also has a prominent literary agency, another that manages and presents world-renowned classical musicians, and a firm specializing in the development of golf courses and other recreational amenities for destination resorts.
Among other IMG clients are Wimbledon, the Royal and Ancient Golf Club of St. Andrews, model-actors Elizabeth Hurley and Liv Tyler, renowned violinist Itzhak Perlman, the Kennedy Space Center, and the Smithsonian Institute, Derek Jeter, Vince Carter, Jeff Gordon, Peyton Manning, Rich Gannon, John Madden, and tennis stars Serena and Venus Williams.
More recently, he was given the 2001 PGA Distinguished Service Award, among the highest honors in golf. In June of that year, Ernst & Young named him "Entrepreneur of the Year."
McCormack, who was working at the time he was stricken, is survived by his second wife, former tennis pro Betsy Nagelsen, four children, and seven grandchildren. His three oldest children -- Breck, Todd, and Leslie -- are executives at IMG.
McCormack and Betsy Nagelsen were married in 1986. She is the two-time Australian Open Doubles Champion, Wimbledon Doubles finalist, and U.S. Mixed Doubles finalist.