REX-1 is a character who appears in two episodes of the Teenage Mutant Ninja Turtles (1987 animated series). He is a robot policeman and his name is an acronym for "Robot Enforcement Experiment," the "1" designating his status as the first model produced. His first appearance is in the second season episode, "New York's Shiniest". His only other appearance is in "Leonardo, the Renaissance Turtle".
Created as an experiment to relieve some of the burdens on New York City's human police department, REX-1 was prematurely activated by April O'Neil. Designed to be unwaveringly loyal to the operator of his remote control, he immediately considered April his master and would not leave her side. His designs were stolen by Shredder so he could mass-produce an army of robot cops under his own command. With some help from April and the Ninja Turtles, REX-1 was able to fool the army of evil robots and save the city.
Sometime before his second appearance, he was placed back into storage at a police warehouse. April and Leonardo reactivated him in order to help stop a rogue robot named LEX, who sought to enslave the city with totalitarian justice.