Rex is a male Bernese Mountain Dog who debuted in season eight. He is a pup from the Dino Wilds, a hidden area near Adventure Bay where ancient dinosaurs still live. Rex has the ability to speak to dinosaurs, which he uses in rescue missions.
Rex has mostly black fur, visible on his legs, tail, and the top of his head. He also has patches of white fur on his paws, neck, and face, and brown fur around his ankles and on his cheeks. He typically wears a light blue helmet and vest, with green ribbing running down the front of his chest and under his belly and green accents. Rex's back legs don't function properly, requiring him to use a wheeled walker that connects to his vest and pup pack and allows him to move about with agility.