Cars 2 was the first Pixar Cars film to feature Mater as the main character.
The original Cars centers primarily on Lightning McQueen’s emotional change after he becomes stranded in Radiator Springs. Cars 2 shifts the focus toward Mater, who travels internationally with McQueen and is mistaken for a secret agent during the World Grand Prix.
This change also changes the genre. Cars 2 combines racing with a spy adventure inspired by international espionage films. Mater’s innocence and unusual behavior drive much of the comedy, while his accidental involvement in the investigation supplies the story’s central viewpoint.
Cars 3 returns the main dramatic focus to Lightning McQueen and his struggle with a younger generation of racers. Cars on the Road is a later television series, not a feature film. The distinction makes Cars 2 the correct answer for the first feature centered on Mater.