Superman-X
When aliens whom Superman once met when he was known as Superboy arrive on Earth to ask for help in dealing with a threat to their world and civilization, the Man of Steel agrees to help them and in return one of the aliens stays behind on Earth to take over Superman's job as a superhero on Earth while Superman is away helping the aliens. The news media begins to refer to this new alien Superman as Superman-X. Superman-X begins to perform amazing super-feats, including curing deadly diseases which led the people of Earth to think that perhaps Superman-X is an even better superhero than Superman himself, Superman-X becomes overzealous with the use of his powers which leds to riots breaking out as a result of people trying to get him to heal them as well. That is until Lois Lane and Jimmy Olsen show Superman-X a news story in which a child with polio and leg braces is killed in the chaos of people trying to get to the Superman-X at the gates of a hospital. Superman-X believes it and thus heartbroken and horrified decides to leave Earth forever. The tape, it turns out was nothing but a fake and no one actually died, although the chaos was real. The real Superman soon returns to Earth after his outer-space adventure (S No. 418, Apr 1986: "The Replacement!")
