Guillermo Vilas, Argentinian tennis player
Guillermo Vilas (Spanish: [ɡiˈʝeɾmo ˈβilas]; born 17 August 1952) is an Argentine former professional tennis player, No. 1 of the Grand Prix seasons in 1974, 1975 and 1977, who won four Grand Slam tournaments, one year-end Masters, nine Grand Prix Super Series titles and 62 total 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 that 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.Known for his prolific match play, especially on clay, he became the second man to win more than 900 matches in the Open Era, and his number of match-wins on clay (659) is by far the most of the era. His peak was the 1977 season during which he won two major titles (both on clay), had two long match win streaks of 46 all-surface and 53 on clay, and finished with an Open Era record of match wins. In 2016, The Daily Telegraph ranked him as the 3rd best male clay-court player of all time, behind Rafael Nadal and Björn Borg. In 2018, Steve Tignor for Tennis Magazine ranked him as the 16th greatest tennis player of the Open Era.

Historical and statistical studies presented in 2015 by Argentinian journalist Eduardo Puppo and Romanian mathematician Marian Ciulpan concluded that Vilas should have been No. 1 in the old ATP ranking system for seven weeks between 1975 and 1976. The ATP Tour and its chief executive at that time, Chris Kermode, although not refuting the data, decided not to officially recognize Vilas. The controversy is still in the legal stage. In October 2020, Netflix released a documentary film about the Vilas case titled "Guillermo Vilas: Settling the Score".