In the 2008 film adaptation of the manga and anime, Rex Racer is portrayed by Scott Porter while Racer X is portrayed by Matthew Fox. The relationship between Rex and young Speed is built considerably with Speed looking up to Rex as a role model and learning to drive from his older brother. Rex drives the Mach 5 in the film and gives it to Speed when he leaves Pops' racing team to drive for corporate interests. As a result, in this adaptation Rex does not destroy the car he drove for Pops (the Mach 4) and is portrayed as a reckless and cheating corporate driver responsible for numerous crashes before being killed at the entrance of the Ice Caves in the Casa Cristo cross country race.
When Racer X appears in the film, he has been working as a gun for hire and is feared by many drivers, sponsors, and corporate interests. Racer X works with Inspector Detector tracking the corruption that has taken over racing, and contracts Speed to work with him and Taejo Togokhan (a key witness in the case against Royalton's corruption) in the Casa Cristo that season. Speed begins to suspect that Racer X is in fact Rex, noting that the masked racer appeared exactly two years after his brother died in "The Crucible" and exhibits the same driving styles.
After Taejo Togokhan reneges on the proposed takedown of Royalton Industries after Casa Cristo, Speed recklessly races the Mach 5 at the track where Rex took him to drive when he was younger. Racer X appears and Speed confronts him about his suspicions, especially due to the two's similar driving styles and the fact that Racer X found him at that particular race track. Removing his mask, Speed is depressed to learn that Racer X is not his brother. However, as the film closes the truth about Rex and his work before his "death" is revealed and he is shown faking his death in the caves, detonating his car and undergoing cosmetic surgery afterwards to alter his appearance in order to take on the corruption without bringing harm to his family. In the end, as in all his other versions, Racer X is Rex Racer. When Inspector Detector asks Rex whether he made a mistake by leaving his family, Rex responds to him saying that "If I did, it's a mistake I'll have to live with."