(documented or estimated)
Argentine Guillermo Vilas, born 17 August 1952, was the No. 1 of the Grand Prix seasons in 1974, 1975 and 1977, and won four Grand Slam tournaments, one year-end Masters, and a total of 62 ATP titles. World Tennis, Agence France-Presse and Livre d'or du tennis 1977 (Christian Collin-Bernard Ficot), among other rankings and publications, rated him as world No. 1 in 1977 (while others ranked Björn Borg or Jimmy Connors No. 1). In the ATP computer rankings, he peaked at No. 2 in April 1975, a position he held for a total of 83 weeks. He was inducted into the International Tennis Hall of Fame in 1991, two years after his first retirement.