Lyle Norg
The first Invisible Kid was Lyle Norg, an early member of the Legion who gained his powers from a chemical serum he invented. He first appeared in Action Comics #267. His scientific aptitude meant he got along well with the super-intelligent Brainiac 5. His abilities made him a valuable asset to the Legion Espionage Squad, of which he was a permanent member. Norg also served one term as Legion Leader. He was killed by the monster Validus of the Fatal Five in Superboy and the Legion of Super-Heroes #203 (July/August 1974).
Many years later, during the "Five Year Gap" following the Magic Wars, Earth fell under the covert control of the Dominators, and withdrew from the United Planets. A few years later, the members of the Dominators' highly classified "Batch SW6" escaped captivity. Originally, Batch SW6 appeared to be a group of teenage Legionnaire clones, created from samples apparently taken just prior to Ferro Lad's death at the hands of the Sun-Eater (Since Lyle was Legion leader at that time, the members of Batch SW6 were led by the teenage Lyle). Later, they were revealed to be time-paradox duplicates, every bit as legitimate as their older counterparts. After Earth was destroyed in a disaster reminiscent of the destruction of Krypton over a millennium earlier, a few dozen surviving cities and their inhabitants reconstituted their world as New Earth. The SW6 Legionnaires - including their version of Invisible Kid - remained.
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