In Pixar's Cars, Rust-eze is the sponsor whose logo appears on Lightning McQueen before his first Piston Cup win.
Rust-eze is a fictional brand of rusty-bumper ointment owned by brothers Rusty and Dusty Rust-eze. McQueen initially dislikes the sponsor's appearance and dreams of replacing it with the prestigious Dinoco branding. His attitude changes as he develops a personal connection with the Rust-eze team.
The sponsorship becomes important at the film's conclusion. After McQueen helps The King instead of taking an easy victory, Dinoco offers him a sponsorship opportunity, but he chooses to remain with Rust-eze. The decision shows that loyalty and relationships matter more to him than status.
Dinoco is the most common mix-up because its blue branding is associated with The King and is McQueen's hoped-for upgrade. Rust-eze, however, is the sponsor on McQueen's original racing livery.