John Donald Budge (June 13, 1915 – January 26, 2000) was an American tennis player. He is most famous as the first tennis player—male or female—to win all four Grand Slam tournaments in one year and complete the Grand Slam. Budge was the second man to complete the career Grand Slam, after Fred Perry. He won ten majors, of which six were Grand Slam events (consecutively, a men's record) and four Pro Slams, the latter achieved on three different surfaces. Budge is considered to have had one of the best backhands in the history of tennis, with most observers rating it better than that of later player Ken Rosewall.

Budge is also the only man to have achieved the Triple Crown (winning singles, men's doubles and mixed doubles at the same tournament) on three separate occasions (Wimbledon in 1937 and 1938, and the US Championships in 1938), and the only man to have achieved it twice in one year. Budge was the world Number 1 amateur in 1937 and 1938 and world Number 1 professional in 1939, 1940 and 1942.

Budge was born in Oakland, California, the son of Scottish immigrant and former footballer John "Jack" Budge, who had played several matches for the Rangers reserve team before emigrating to the United States, and Pearl Kincaid Budge. Growing up, he played a variety of sports before taking up tennis at the age of 13 at the urging of his elder brother, Lloyd, who played tennis for the University of California team. He also had an elder sister. He was red-headed, tall and slim, and his height would eventually help what is still considered one of the most powerful serves of all time. Budge studied at the University of California, Berkeley, in late 1933 but left to play tennis with the U.S. Davis Cup auxiliary team.

Accustomed to hard-court surfaces in his native California, Budge had difficulty playing on the grass courts in the east.

Budge reached the semi-finals of the West Canada championships in July, where he lost in five sets to Henry Prusoff. "The Oakland youngster carried brawny Hank Prusoff of Seattle to five sets, surprising most of the onlookers, including the tournament favorite from Puget Sound...Budge playing a calm and collected game all the way and letting the hardhitting Prusoff make the errors. The chop stroke of the Seattle man worked to perfection, particularly In the last set, and he always seemed to have something in reserve."

At the Del Monte championships in May, Budge beat Wallace Bates in straight sets in the final. In July, Budge beat John Murio in the final of the California State championship. "Tennis fans will be talking for days of the men's singles event and of Budge, whom the experts candidly admit "has everything". Not only has he the strokes of a champion, but the presence and strategy of one far beyond his years. Murio's most burning drives failed to ruffle one of the flaming red hairs on his head". In the final of the Colorado championships in Denver in July, Budge beat Jack Tidball in five sets.

Budge beat Bud Chandler in the final in five sets to retain his California State championship title in June. "Chandler went to the net often throughout the match, while Budge elected to play a baseline game almost exclusively, going to the webbing only when forced to by chop or cross court shots; Chandler, exhausted after his gruelling five-set match with John Murio in the semi-final on Saturday, fought largely on his nerve against the Champion, and at the end of yesterday's strenuous competition again was completely exhausted."

Budge beat Gene Mako in the final of the Palm Springs tournament in April. Budge beat Frank Shields in the final of the Newport Casino tournament in August. In the final of the Pacific Southwest tournament in September, Budge was leading 2 sets to 1 against Roderich Menzel, when Menzel retired, in order to preserve his energy for a mixed doubles match. Budge beat Bobby Riggs in the final of the Pacific Coast championships in October.