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Superman: Earths
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Superman is most vulnerable to Kryptonite, mineral debris from Krypton transformed into radioactive material by the forces that destroyed the planet. Exposure to Kryptonite radiation nullifies Superman's powers and immobilizes him with pain; prolonged exposure will eventually kill him. The only mineral on Earth that can protect him from Kryptonite is lead, which blocks the radiation. Lead is ... the only known substance that Superman cannot see through with his x-ray vision. Kryptonite was first introduced to the public in 1943 as a plot device to allow the radio serial voice actor, Bud Collyer, to take some time off.[54] Green Kryptonite is the most commonly seen form but writers introduced other forms over the years, such as red, gold, blue and black, each with its own effect.[77]
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Controlled by the parasite, Superman attempted to destroy the Justice League Unlimited and take over the Earth. However, through the efforts of Bruce Wayne, Terry McGinnis and the League, the parasite was defeated and Superman regained control of himself. Terry McGinnis told Superman that he declined his offer to join the Justice League. Proud of Terry, Superman told Terry that he is like Bruce Wayne.
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As time went on, Superman's grip on reality began to break down, causing his behavior to be even more erratic. All of this was because the real culprit was Brainiac, who had recovered from his vegetative state on New Genesis and was returning to Earth.[74] When Superman finally learns what is going on, he confronts Brainiac in the streets of Metropolis, battling the villain until Brainiac is convinced he is about to lose, at which point the personality of Milton Fine reasserts itself and the villain is lead away.[75]
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In September 1949, Superman employs a Superman robot in an elaborate scheme to dupe a band of aliens from the planet Uranus into believing that all earthlings are actually robots. Superman makes his robot appear lifelike by manipulating it like a puppet at invisible super-speed while employing ventriloquism to make it talk (WF No. 42, Sep 1949: "The Alphabetical Animal Adventure!").
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The basic tenant is still there, that Superman came from Krypton to Earth to survive a calamity. At first, there was no mention of how Superman got his powers. Later it was decided that the people of Krypton all had powers like Superman, but that caused problems. It was finally written that Kryptonians live under a red star and when they are exposed to light from a yellow star, their powers emerge.
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In the logic of this latest refinement, all Kryptonian objects acquire indestructibility in the yellow-sun environment of Earth, and all native Kryptonians - such as Supergirl or Krypto the Superdog - acquire super-powers identical to Superman's. However, the indestructibility of these objects and the super-powers of the various Kryptonian survivors remain proportional to what they would have been had they remained in their native Kryptonian environment. Superman is stronger than Supergirl, for example, just as an ordinary human male is normally stronger than his female counterpart. Similarly, a Kryptonian gorilla on Earth would be stronger than Superman, just as an ordinary gorilla is more powerful than an ordinary man.
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