In Pixar's Cars 3, Cruz Ramirez uses racing number 51 when she races for Dinoco.
Cruz begins the film as Lightning McQueen's high-tech trainer at the Rust-eze Racing Center. Although she has racing ability, she initially doubts whether she belongs in the competitive world of the Piston Cup.
After Lightning encourages Cruz to pursue her own racing ambitions, she enters the Florida 500 in his place. She adopts the Dinoco-sponsored identity and number 51, connecting her with the famous racing team previously associated with The King.
The number is easy to confuse with other important Cars numbers. Lightning McQueen is number 95, The King is number 43, and Chick Hicks is number 86. Cruz's number 51 therefore marks her own Dinoco racing identity rather than a change to Lightning's number.