Doc Hudson used racing number 51 in Pixar’s Cars backstory.
Before becoming Radiator Springs’ doctor and judge, Doc was the Fabulous Hudson Hornet, a highly successful stock-car racer. His number 51 appears in historical references and on imagery connected with his racing career.
Doc’s fictional achievements echo the real Hudson Hornet’s importance in early stock-car racing. The real car won major NASCAR races in the early 1950s and became famous for its handling and “step-down” design, which gave it a lower center of gravity.
In Cars, Doc’s racing career ended after a serious crash and a loss of respect from the racing establishment. He later helps Lightning McQueen understand racing discipline and the value of experience. His number is distinct from McQueen’s 95, The King’s 43, and Chick Hicks’s 86.