Guillermo Vilas is an Argentine former professional tennis player. He was the world No. 1 of the Grand Prix seasons in 1974, 1975 and 1977. He won 62 singles titles and 16 doubles titles during his career, including four singles major titles and the 1974 Tour Finals. World Tennis, among other rankings and publications, rated him as world No. 1 in 1977. In the computerized ATP rankings, he peaked at No. 2 in April 1975, a position he held for a total of 83 weeks, although some have argued that Vilas should have been ranked No. 1 for at least 10 weeks, particularly in 1977 when he won two majors. He was inducted into the International Tennis Hall of Fame in 1991, two years after his first retirement.