He was voiced by Edward Norton
He is much more passive and is the first to suggest to rescue and not eat The Little Pilot (Atari). He frequently insists on democracy, and while he and Chief butt heads, Chief often ends being outvoted, as the other dogs agree with Rex.
His original owners owned a cushion and a heat lamp. He frequently states that he has 'had enough of this', but can find no answer for how to get off Trash Island or away from Chief.
He has a big light brown nose that is in the shape of an upside down triangle. Two pointed ears. A dirty, black and white collar with a yellow stripe that runs along the middle of it, that says 'REX' on its square-shaped tag. The collar having a tiny, metal bone hanging off of it.
Rex had been deported to Trash Island after he had been tested 100% for the Dog-Flu. He found Chief, Duke, Boss, and King while on the island, causing them all to make a pack. Rex was a house dog, Rex saying that he used to sleep on a beanbag that lied next to an electric space heater.