Metalo of Earth-2
Metalo is the criminal alias of mustachioed George Grant. Grant possessed awesome power, a renegade inventor --discoverer of "the most powerful metal on Earth" as well as a miraculous "strength serum"-- who, clad in a special armored suit of his own design, is impervious to bullets, can fly through the air, and possesses monumental super-strength equivalent to Superman's.
Operating from a subterranean hideaway beneath the main tent of the Farnham Circus , somewhere on the Metropolis waterfront, Metalo stuns the city with a series of spectacular crimes --including the theft of an entire mail car from the Metropolis train terminal, and an attempt to extort $5,000,000 from the city's businessmen by threatening to destroy Metropolis --until finally, in a climactic encounter with Superman, "the very mountains tremble and are rent asunder by the colossal battle of these two super-powerful opponents ...!"
Believed dead after plummeting into a yawning lava-filled crevice at the peak of the awesome battle, Metalo manages to cling to an outjutting rock and although thwarted in his evil undertakings, to survive (WF No. 6, Sum 1942: "Man of Steel versus Man of Metal!").
In April 1982, the Superman of Earth-2 is secretly hit with a ray beam by Metalo. Less than 24-hours later, Superman and Lois Kent are surprised to discover that Superman's powers have been decreased considerably, to the point where "leaping only an eight of a mile," "hurdling a 20-story building," and running "about 70 miles an hour" is the best he can do. Outmatched in terms of strength by Metalo, Superman must rely on his unaffected heat-vision to temporarily fend off his enemy.
Reduced to driving a car to his mountain retreat [see The Secret Citadel], Superman engages Lois as a personal trainer to help rebuild his strength with the aid of "the world's most amazing gymnasium." Noting that, "it took years to build my physique to what it is today," Superman nevertheless embarks on a "crash-program" of weight-lifting, running, gymnastics, and finally flying, until he looks "more powerful than ever." Handily defeating Metalo in a rematch, the reinvigorated Man of Tomorrow is pressed into service ghost-writing his wife's report on the Metalo encounter, Lois being exhausted "after two days of training" Superman back into shape (SF No. 217/1: "Back to Square One!").