Ordinary Guy was a human native to the planet Mertz. His name derived from the fact he was the only person on Mertz who didn't have superpowers. As Mertz's only normal human, Ordinary Guy was constantly being "rescued" by his neighbors from "dangerous" situations. He eventually grew tired of this and disappeared, prompting the heroes to seek out Comet Guy's old friend Darkwing Duck as a replacement.
In reality, Ordinary Guy had taken on a supervillain persona, Not-So-Ordinary Guy, and invented a large ray gun which would steal the superpowers of all of Mertz's heroes. He then turned the device on himself, absorbing all of the stolen powers and becoming huge and muscular. In this form, he renamed himself Extraordinary Guy. Darkwing, already lacking powers, used the machine on himself and became big enough to battle Extraordinary Guy. The two fought and eventually grew so huge they stood astride Mertz itself and used surrounding planets and stars as weapons.
The battle ended when Darkwing reversed the machine against Extraordinary Guy, but not himself, turning the villain back into a normal, powerless human, and returning the superpowers to their rightful owners. Ordinary Guy almost went spinning helplessly off into space, but he was rescued at the last second by Darkwing, who told him a true hero saves the villain.