The simple answer is that they are currently different branches of the same family tree.
The Professional Golfers Association (PGA) of America is composed of some 28,000 teaching and club professionals. The PGA of America dates to 1916 and originally also included playing professionals.
The PGA TOUR spun off from the PGA of America in December 1968. Originally called the “Tournament Players Division,” it was renamed the PGA TOUR in 1975. The PGA TOUR is now the organizing body for professional tournament circuits including the PGA TOUR, Champions Tour, Web.Com Tour, PGA Tour Canada, PGA Tour Latinoamérica, and PGA Tour China.
The PGA of America was founded in 1916 at the prompting of department store magnate Rodman Wanamaker, who believed that an association of golf professionals would bolster the sales of golf equipment. The initial meeting was held on January 17 at the Martinique Hotel in New York. A February meeting was held at Wykagyl Country Club in New Rochelle, New York. On April 10, 1916, thirty five top golf professionals signed the organization’s constitution and bylaws.
The first PGA Championship was held October 10 – 14 at Siwanoy Country Club in Bronxville, new York. It was won by Jim Barnes. Wanamaker donated a trophy and the purse of $2,580. To this day, the PGA Championship trophy is known as the Wanamaker Trophy.
As originally conceived, club professionals, teaching pros and touring professionals alike belonged to the PGA of America. Over the years, however, tension arose between club pros, and those who made their living through tournament play. The disputes escalated as the game’s popularity grew through the 1950s and 1960s with the accompanying rise in purses and television revenues.
In his autobiography, Arnold Palmer wrote: “As crass as it sounds, the issue was really money—more precisely, television money.”
Finally, in 1968, prominent tour players, including Jack Nicklaus, Gardner Dickinson, Doug Ford, and Frank Beard broke from the PGA to form the American Professional Golfers, Inc. Others followed. By December of that year, however, a compromise was reached, and the PGA Tournament Players Division was formed. The new, independent division was headed by Joe Dey. In 1975, under commissioner Deane Beman, the name was officially changed to the PGA TOUR.
While the PGA TOUR runs dozens of golf tournaments, it does not “own” or run the PGA Championship. The PGA Championship is the property of the PGA of America, and the field includes the best of that organization’s club professionals.
The Ryder Cup is the joint property of the PGA of America and Ryder Cup Europe, which is a joint venture of the European Tour, the PGA of Great Britain and Ireland, and the PGA of Europe.
The President’s Cup is owned by the PGA TOUR.
On a side note, the PGA TOUR does not “own” or run any of golf’s four majors. The Masters is run by Augusta National, the US Open by the United States Golf Association, the Open Championship by the Royal and Ancient, and the PGA Championship by the PGA of America.
The lack of control over any of Golf’s recognized majors explains the PGA TOUR’s efforts to position the Players’ Championship (which they DO own) as the unoffical “fifth major.”