Dennis Ralston, a five-time Grand Slam doubles champion who was one of the initial players signed to the professional World Championship Tennis tour in the 1960s and a member of the sport's Hall of Fame, died Sunday. As a singles player, Ralston lost to Spain’s Manuel Santana in three sets in the 1966 Wimbledon final. He paired with Rafael Osuna of Mexico to win Wimbledon in 1960 as a 17-year-old. He and fellow American Chuck McKinley won titles at the U.S. national championships in 1961, ’63 and ’64. The WCT tour helped commercialize the sport, instituting a tiebreaker system and emphasizing its prize-money structure and a bonus pool to attract top players.