Björn Rune Borg (Swedish pronunciation: [ˈbjœːɳ ˈbɔrj] (listen); born 6 June 1956) is a Swedish former world No. 1 tennis player. Between 1974 and 1981, he became the first man in the Open Era to win 11 Grand Slam singles titles with six at the French Open and five consecutively at Wimbledon.

Borg won four consecutive French Open titles (1978–81) and is 6–0 in French Open finals. He was the first man since 1886 to contest six consecutive Wimbledon finals, a record surpassed by Roger Federer's seven consecutive finals (2003–09). He is the only man to achieve the Channel Slam three times. Borg contested the French Open, Wimbledon and US Open finals in the same year three times (1978, 1980–81). He won three major titles without dropping a set during those tournaments. However, he never won the US Open despite four runner-up finishes.

Borg also won three year-end championships and 16 Grand Prix Super Series titles. Overall, he set numerous records that still stand. He was ATP Player of the Year from 1976 to 1980, and was the year-end world No. 1 in the ATP rankings in 1979 and 1980 and ITF World Champion from 1978 to 1980. Borg is the only Swede, male or female, to win over 10 majors. Borg unexpectedly retired from tennis in 1981, at the age of 25. He made a brief and unsuccessful comeback in 1991.

Borg is widely considered one of the all-time greats of the sport. He was ranked by Tennis magazine as the sixth-greatest male player of the Open Era. His rivalry with John McEnroe is considered one of the best in the sport's history, and their meeting in the 1980 Wimbledon final is considered one of the greatest matches ever played. A teenage sensation at the start of his career, Borg experienced unprecedented stardom and consistent success that helped propel the rising popularity of tennis during the 1970s. As a result, the professional tour became more lucrative, and in 1979, Borg became the first player to earn more than US$1 million in prize money in a single season.