Psi-Phon and his colleague Dreadnaught were two highly sophisticated lifeforms sent as spies to find out Earth's capacity to withstand a fullscale invasion.
He watched Superman, unobserved, using his powers. He secretly began to shut the Man of Steel's powers and confronted him with an energy charged Dreadnaught. Superman sent out distress signals for help. Aquaman, Captain Marvel, Elongated Man and Martian Manhunter responded and soon lost most of their powers. Superman realized what Psi-Phon was doing and that his powers were not actually stolen, just unavailable. Superman believed that there could create a power overload by having Psi-Phon channel more and more power to Dreadnaught. Superman used his Clark Kent persona to defeat Dreadnaught when he could not use his powers, utilizing a force field he borrowed from Emil Hamilton. Defeated, Psi-Phon and Dreadnaught self-destructed leaving a cloud of vapor.
Powers and Abilities
Psi-Phon was designed by an unknown extraterrestrial race to analyze the brains of super-powered beings and shut down that individual from using his power psionically. He would then transmit energy into the much larger Dreadnaught, who had the ability to duplicate that individual's powers. Psi-Phon had to watch his target use the powers before he could shut them off.