The 9th International 500-Mile Sweepstakes Race was held at the Indianapolis Motor Speedway on Monday, May 30, 1921.

Raffaele "Ralph" DePalma was an American racing driver who won the 1915 Indianapolis 500. His entry at the International Motorsports Hall of Fame estimates that he won about 2,000 races. DePalma won the 1908, 1909, 1910, and 1911 American AAA national dirt track championships and is credited with winning 25 American Championship car races. He won the Canadian national championship in 1929. DePalma estimated that he had earned $1.5 million by 1934 after racing for 27 years. He is inducted in numerous halls of fame. He competed on boards and dirt road courses and ovals.