Ilie Theodoriu Năstase is a Romanian former world No. 1 tennis player. He held the top singles spot from 23 August 1973 to 2 June 1974, and was the first man to hold the position on the computerized ATP rankings. Năstase is one of the 10 players in history who have won over 100 total ATP titles, with 64 in singles and 45 in doubles. Năstase won seven major titles: two in singles, three in men's doubles and two in mixed doubles. He also won four Masters Grand Prix year-end championship titles. He was the first professional sports figure to sign an endorsement contract with Nike, doing so in 1972. Năstase wrote several novels in French in the 1980s, and was inducted into the International Tennis Hall of Fame in 1991.

The PIF ATP Rankings are the merit-based method used by the Association of Tennis Professionals (ATP) for determining the qualification for entry as well as the seeding of players in all singles and doubles tournaments. The first rankings for singles were published on 23 August 1973 while the doubles players were ranked for the first time on 1 March 1976. Ranking points are awarded according to the stage of tournament reached, and the prestige of the tournament, with the four Grand Slam tournaments awarding the most points. The rankings are updated every Monday, and points are dropped 52 weeks after being awarded. Novak Djokovic is the current men's singles world No. 1.