Guillermo Vilas is an Argentine former professional tennis player. Vilas was the world No. 1 of the Grand Prix seasons in 1974, 1975 and 1977. He won four major titles, the year-end championships, and 78 career singles titles overall, 62 of which were ATP titles. World Tennis, Agence France-Presse and Livre d'or du tennis 1977, 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 2 majors. He was inducted into the International Tennis Hall of Fame in 1991, two years after his first retirement.

The ATP Finals is the season-ending championship of the ATP Tour. It is the most significant tennis event in the men's annual calendar after the four majors, as it features the top eight singles players and top eight doubles teams based on their results throughout the season. The eighth spot is reserved, if needed, for a player or team who won a major in the current year and is ranked from ninth to twentieth.