Rex is a local dojo owner in Preston, Idaho. He owns the Rex Kwon Do martial arts center, which teaches a style of self defence, but Rex is somewhat of a poor trainer, who uses weaker people for his examples, like in his commercial, and Kip, and even then he uses cheap tricks to fight. He also verbally abuses people, like Napoleon. He is portrayed by Diedrich Bader.
Rex advertises his dojo on TV, and claims his students will learn "the strength of a grizzly, the reflexes of a puma, and the wisdom of a man." This catches Kip's attention, who goes over to the dojo with Napoleon to try it out. There, Rex calls Kip up for a demonstration. Kip is eager to show off his skills, but by the end of the demonstration, Kip has realized that Rex Kwon Do will be too hard for him, when Rex physically overwhelms him. Rex then explains some rules, mocking Napoleon's fashion style and calls his clothes "like Peter Pan," ending any chance of Napoleon joining. Kip and Napoleon leave, calling his dojo "a rip-off."
Later, Uncle Rico attempts to sell breast enhancing products to Rex's wife, Starla. Rex walks in and finds Uncle Rico in a very awkward position. Rex then beats up Uncle Rico, and breaks his left arm.
"My name is Rex, and if you study with my eight-week program, you will learn a system of self-defense that I developed over two seasons of fighting in the Octagon. It's called Rex Kwon Do!" - Rex's introduction to his trial students
"Bow to your Sensei. Bow to your Sensei!" - to Kip
"Now I'm gonna give you one chance. One chance, people. Gimme your best shot." - Rex challenging Kip
"Okay, now watch this. I'm just gonna break the wrist and walk away. Break the wrist, walk away." -Rex, when he hits Kip in the wrist
"Rex Kwon Do, we use the buddy system. No more flying solo. You need somebody watching your back at all times!" - Rex's first rule
"You're gonna learn to discipline your image. You think I got where I am today because I dress like Peter Pan here? (points to Napoleon) Take a look at what I'm wearing, people. Do you think anybody wants a roundhouse kick to the face while I'm wearing these bad boys? Forget about it." - Rex's second rule
"My students will learn about self-respect. Do you think anybody thinks I'm a failure because I go home to Starla at night? Forget about it!" - Rex's third rule
"Come here, boy!" - When Rex finds Uncle Rico with Starla