Rust-eze is the fictional sponsor displayed on Lightning McQueen in Pixar's Cars.
Rust-eze is introduced as a bumper-ointment company whose sponsorship supports Lightning while he competes in the Piston Cup. Its founders, Rusty and Dusty Rust-eze, discover and promote him after his forced stay in Radiator Springs.
The sponsor's most visible branding is the Rust-eze logo on Lightning's red body. The partnership is initially embarrassing to Lightning because he wants a prestigious racing image, but it becomes an important part of his career and identity.
Dinoco is the most common alternative answer because it is another major fictional racing brand in the series. However, Dinoco sponsors The King in the first film and later becomes associated with Lightning after the championship outcome. Rust-eze is Lightning's original main sponsor, while later films show changes in his racing career and sponsorship arrangements.