Rex Owen is Max's best friend. Rex was found as an infant by paleontologist Dr. Owen in an egg-like container within a dinosaur exhibit in New York. Rex is now 12 and has been left with Max and his family while his father goes searching for fossils with Dr. Owen being a family friend of the Taylor family. It is revealed in one episode that Rex was left at Max's house because his father wanted him to be near a real family. Rex's partner is a Carnotaurus he named Ace. Rex also owns most of the fire and wind dinosaurs. Rex is a good-hearted boy and is relatively quiet, but also quite short-tempered from the beginning. At the end of the first series, it is revealed that Rex's real parents are Dr. Ancient and Dr. Cretacia and Rex reunites with them. In the finale, Rex, the Alpha Gang, Seth, Chomp, Ace, Paris and the Ancients return to the year 2126.
Rex played Kovu in The Child King 2: Max's Pride
Rex played Dale in Max and Rex Rescue Rangers
Rex played Genie in Maxladdin (DinosaurKingRockz), Maxladdin 2: The Return of Merlock, and Maxladdin 3: Maxladdin and the King of Thieves
Rex played Duckworth in ChildTales, and ChildTales the Movie: Treasure of the Lost Lamp
Rex played Andrew in Sailor Zoe, and Sailor Zoe (VIZ)
Rex played Simon Seville in Max and the Children (1983)
- In Dinosaur King (DinosaurKingRockz Style) he is played by Po.