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.

The 5th International 500-Mile Sweepstakes Race was held at the Indianapolis Motor Speedway on Monday, May 31, 1915. The traditional race date of May 30 fell on a Sunday, but race organizers declined to schedule the race for Sunday. The race was set for Saturday May 29, but heavy rains in the days leading up to the race flooded the grounds and made some roads leading to the track impassible. Officials decided to postpone the race until Monday May 31 in order to allow the grounds to dry out. Speedway management would maintain their policy to not race on Sundays until 1974.