Rex is a half mechanical tyrannosaurus rex, half organic.
He is known to be the self-proclaimed leader of the Animal Mechanicals, in which the others agree to it. Like the others, Rex can transform into his Mechana-form, which is Mechana-Strong. He often guides missions and tells the others what they have to do. Besides having a big heart, he also has a big appetite.
Rex is always hungry and will try to do anything to get food when he sees one, but most of the times he doesn't realize the troubles he's been causing and will apologizes right away. Sometimes, even the other Animal Mechanicals members have to stop him from doing so.