Guillermo Vilas (Spanish pronunciation: [ɣiˈʃe̞ɾmo ˈʋiläs]; born 17 August 1952) is a retired professional tennis player from Argentina, N°1 of the Grand Prix tennis circuit's Season in 1974, 1975 and 1977, who won four majors, one Master and 62 ATP titles. He was inducted into the International Tennis Hall of Fame in 1991. 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 659 wins on clay are 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 134 match wins. In 2005, Tennis magazine ranked him as the 15th-best male player of the preceding 40 years. He also popularized the between-the-legs tweener shot, also known as the "Gran Willy" in his honor.