Thaddeus Thawne II, also known as Thad Thawne, is a clone of The Flash created by the future president of Earthgov as a weapon, who later became Kid Zoom, and is currently Professor Zoom.
Thad was created from the genetic material of Bart Allen by his "father", the original Thaddeus Thawne, who was president of Earthgov at the time, as an ageless weapon which could be used to attack the Allen family without the public knowing. Thad was placed in a virtual reality designed to force his mind into believing that the Allens and all other "heroes" (mainly the members of the Legion of Superheroes) were his mortal enemies. Even outside of the virtual reality, Thad was under constant pressure from his father, which inevitably drove him insane. When Bart Allen was rescued from Earthgov by Barry Allen, Thad was discovered by Barry, who was unfortunately incapable of saving him from this torment.
When Bart was taken to the 20th Century, President Thawne had Thad sent back as well. Thad first studied Bart, taking his time to replicate the speedster's personality, and would soon battle Kid Flash for the first time, taking him and trapping him within the Speed Force. Thad then took Bart's identity and fooled even the Teen Titans into believing he was Bart. Unfortunately for Thad, the former Flash, Barry Allen, had managed to push Bart from the Speed Force. Bart reclaimed his identity and exposed Thad for the fraud he committed. Thad admitted to his crime, happy to be free from the identity of his enemy, but he continued to antagonize Bart as Kid Zoom, the reverse Kid Flash.
Though Bart grew up and became the new Flash, Thaddeus was stuck as a teenager due to his decelerated aging. Learning from his (literal) partner-in-crime, Eobard Thawne, Thaddeus was taught that he could use a new energy source, the Negative Speed Force, to manipulate his age to match Bart's. Doing so, he became the new Professor Zoom (as Eobard left for the future to continue his never-ending battle with Barry), and continued his war against the Allens. Thad joined the Injustice League and became one of the greatest enemies to the Flash Family in history.
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