Doc Hudson had won three Piston Cups before his crash in Pixar's Cars.
The film explains that Doc was a celebrated racing champion who earned three Piston Cup victories in the early 1950s. His career changed after a crash left him sidelined. When he returned, racing officials and fans treated him as obsolete, and he withdrew from competition rather than accept a reduced role.
Doc eventually settled in Radiator Springs, where he became the town's doctor and judge. Lightning McQueen's arrival forces him to confront his abandoned racing identity. Doc first resists helping the rookie, but later becomes Lightning's crew chief and mentor.
The Piston Cup is a fictional racing championship inspired by real American stock-car competition. Doc's three victories are sometimes confused with Lightning McQueen's championship totals, but the number belongs specifically to Hudson's pre-crash career.