Rex first appears in Ty 1 where he teaches Ty to swim, gives him the aquarangs, and sends him out to search for his girlfriend Elle.
He often helps Ty in many missions. In Ship Rex, Rex taught Ty to swim and then asked him to go find his girlfriend, Elle. Rex also gave Ty the aquarangs. When Ty finds Elle she gives him a red thunder egg. She is seen again in Ty 1 in Rex Marks The Spot where with Rex trying to steal Parrotbeard's treasure from the abandoned mine and Rex asks Ty to boomerang the octopus's tentacles. Rex goes first, then Elle, then Rex again. Ty gains a green thunder egg. Rex appears again in Rex Marks The Spot where he races Ty between the islands and Ty gains a thunder egg. He also appears in Ty 1 in The Bridge Over The River Ty where he teaches Ty how to dive.
Rex and Elle also appear in Ty 2 when Elle asked Ty to take sun screen to Rex. Rex appears in the mini game cart racing for Ty 2 also. Maurie in Ty 2 tells Ty Rex is stuck in the bottom of the bay of a beach surrounded by sharks. Elle told Ty the same thing and Ty had to save him by exploding the sharks in a bunyip. Rex then asked Ty to connect pipes underneath the water because Boss Cass sabotaged the oxygen system. There is a picture of Rex and Elle in concept art in Ty 2.
Night of the Quinkan
Rex appears in Ty 3 in a mini game cart racing where he is one of many playable racers. In Ty 3 Rex wears a light purple striped fedora with light purple pinstripe shirt and light purple shorts.
Role in the series
Rex not only helps Ty with swimming. There are those in The Troupe of Lightning that need it more than anything. But he does have trouble teaching those like Sonic the Hedgehog, and usually needs to aid him when he's drowning.