In Pixar's Cars, Doc Hudson is revealed to be the town's judge and a former Piston Cup champion.
Doc is introduced as the Hudson Hornet who serves as Radiator Springs' judge and physician. He is stern toward Lightning McQueen, especially when Lightning treats the town as an obstacle rather than a community. His authority comes from both his civic role and his experience as a racer.
The film later reveals that Doc was the Fabulous Hudson Hornet, a three-time Piston Cup champion. His racing career ended after a serious crash led the press and officials to overlook him. Although he returned to racing, he was never again treated as a leading competitor, and he eventually withdrew from the sport.
Doc's past explains why he understands racing but refuses to train Lightning at first. He is not the same character as Strip “The King” Weathers, the reigning champion seen in the film's opening race, or Chick Hicks, Lightning's aggressive rival.