Rex is Clyde's dog. He appeared in "Big Gay Al's Big Gay Boat Ride". Stan's homosexual dog Sparky had sex with him, which terrified Rex and made him run away. In the process, this shocked and appalled Stan and Clyde, and left Kenny, Kyle, and Cartman amused. He has since not made any further appearances.
Rex is a gray dog. He has a white snout and slightly darker gray paws.