What type of car is Pixar's character Doc Hudson based on?

Pixar's Doc Hudson is based on the Hudson Hornet.

Doc is identified in Cars as the Fabulous Hudson Hornet, a fictionalized version of the real American car produced by the Hudson Motor Car Company. The character's design draws particularly on the first-generation Hudson Hornet, whose low body and racing reputation made it distinctive among early postwar automobiles.

The real Hudson Hornet became famous in stock-car racing during the early 1950s. Drivers such as Herb Thomas, Tim Flock, and Marshall Teague helped establish the model's competition legacy, and its victories contributed to the nickname “Fabulous Hudson Hornet.” Pixar used that history to create Doc's backstory as a champion who was forced into retirement after a crash. Doc is sometimes mistakenly identified as a generic old sedan, but his specific make and model are central to the character's identity.