In Pixar's Cars, Dinoco is the fuel brand that sponsors The King. The King is the veteran racer Strip Weathers, and Dinoco's sponsorship represents the prestige and success Lightning McQueen hopes to achieve. The blue Dinoco branding is one of the most recognizable visual details in the film.
Rust-eze sponsors Lightning McQueen at the beginning of the story, while Dinoco is associated with The King. After the championship race, McQueen is offered the Dinoco sponsorship but chooses to remain with Rust-eze because of the loyalty shown by its owners, Rusty and Dusty Rust-eze.
Dinoco returns in later Cars stories and is also connected to Pixar's Toy Story through a fictional gas station sign. That cross-film appearance can make the brand seem more familiar than its role in Cars alone. Dinoco is a sponsor and fuel-company brand in the films, not the name of a race, trophy, or character.