Racer X, secretly Rex Racer, is the eldest son of Pops and Mom Racer and Speed and Spritle's older brother. His path diverged after wrecking the experimental Mach 1 during his first professional race at 18. Facing Pops' harsh rejection of his driving, Rex left home, vowing to become the world's greatest racer alone. He adopted the alias "Racer X"—a play on Rex—concealing his identity behind a mask as the enigmatic Masked Racer, allowing him to race while hiding his family ties. Across iterations, Racer X also operates as international secret agent "Agent 9," using racing as cover for missions against corporate corruption and criminal conspiracies. His advanced vehicle, the Shooting Star (numbered 9), links him to intelligence headquarters in Paris. He frequently partners with Inspector Detector, though their organizational connection remains undefined. On the track, Racer X possesses exceptional skill, widely regarded as superior to Speed. Yet, he consistently sacrifices victory, placing second to protect Speed from sabotage or harm, often ensuring his brother wins. The resolution of his hidden identity varies. In the original anime, Speed confronts him near the end. Racer X punches Speed unconscious, confesses his identity to villain Captain Terror, leaves his mask beside Speed as acknowledgment, and abandons racing for full-time espionage. The 2008 film reimagines Rex faking his death during the Casa Cristo 5000 to infiltrate racing corruption undetected. He undergoes facial reconstruction, permanently becoming Racer X. When confronted by Speed, he removes his mask to reveal his altered face, denies being Rex, and continues covert work without family reunion. The spin-off *Speed Racer: The Next Generation* features Speed Racer's firstborn son inheriting the "X Racer" mantle. This X is a talented but fame-driven academy racer piloting the Shooting Star. Manipulated by the antagonistic Shadow Committee, he briefly becomes the villainous "Red Bolt" before ultimately choosing to protect his younger brother, Speed Jr. Racer X's character embodies sacrifice, protection, and unresolved familial bonds. His actions, as Rex or his successor, focus on safeguarding the Racer legacy while operating from the shadows, maintaining distance to fulfill his self-imposed missions.