Doc Hudson raced under number 51 in Pixar's Cars.
Doc is revealed to be the Fabulous Hudson Hornet, a legendary race car who won three Piston Cup championships in the early 1950s. His racing number, 51, appears with the Hudson Hornet's distinctive branding.
The character is voiced by Paul Newman, whose performance gives Doc a reserved and authoritative personality. In Radiator Springs, he serves as the town's doctor and judge before Lightning McQueen discovers his hidden racing history.
Lightning McQueen's number is 95, so those two numbers are often mixed up. Number 43 belongs to The King, while number 86 is associated with Chick Hicks in the original film.