Rex Salazar is a sixteen-year-old,amnesiac EVO with the ability to grow weapons and machines out of his body at will. He was employed as a secret weapon to Providence, a global organization dedicated to protecting the world from rampaging EVOs. After the new changes in Providence, he joined the Providence Defect Group. He later returned to Providence after White Knight became leader of Providence again.
Rex made his first appearance in Ultimate Story 4. Rex was fighting EVOs like he normally does. But one day, the Heartless show up in his world. He tried to fight them but his abilities were shown to have very little effect on them. He then attempted to control the nanites inside them to try and tame them but then found out that there were no nanites. At that instant, Fox and his friends appeared and fought off the Heartless.
After the fight, they introduced themselves to him and told him about everything that had been happening. It was discovered that the Heartless had just recently breached his world and aim to put a stop to them before his world falls into the brink of deterioration just like the others.
After he joined the Keyblade Force, he along with a few other friends of his were pulled out of their world. His friends were seeking refuge within Traverse Town while he stayed in Twilight Town along with the other members of the Keyblade Force.
- Rex is voiced by Daryl Sabara, who played Juni Cortez in the film series Spy Kids. During the first 3 movies, Daryl was still a kid. His role returned in the fourth movie but couldn't star in the main role due to him being too old. The main role were filled in by 2 other child actors who played as different characters in the movie.
- Rex's goggles are based off of the goggles from the Digimon series that were worn by most of the main characters from each of the different series.