Mack is Lightning McQueen's hauler and best friend in Pixar's Cars.
Mack is a red truck who transports Lightning between races. He is loyal and hardworking, but the opening journey to California shows the practical problems caused by Lightning's self-centered behavior. Mack becomes exhausted when Lightning insists on staying awake and then accidentally falls from the trailer.
That incident separates Lightning from his team and sends him toward Radiator Springs. Mack's absence is therefore an important cause of the film's central detour. He later helps reconnect Lightning with the Piston Cup race and remains part of his support team.
Mater is Lightning's closest friend in Radiator Springs, but he is a tow truck rather than Lightning's racing hauler. Luigi and Guido operate the tire shop in Radiator Springs. Because all four characters are strongly associated with Lightning, their distinct roles can be easy to mix up.