Action Man 1990s series background information on both Action Man and Doctor X. I found all this from the website Dr. X|Action Man Wiki|Fandom.
Dr X's real name is Dorian Exler. during his childhood, his parents adopted a younger son named Matthew (who would later be Action Man. Under the tutelage of their father, Dr. Exler, both sons were geniuses from an early age and both were science prodigies. However, Dorian was a bad seed; a born psychopath who ultimately was responsible for deliberately setting a fire which killed his parents. And in the aftermath of his heinous act of patricide, Dorian cleverly made young Matthew think that he was responsible for this "accident".
Each son received an inheritance of a handsome trust fund, so Dorian, using his inherited wealth as seed money, and nurturing it with his raw, genius-level intelligence, ruthlessness and powerlust, not only grew his financial fortune by a multiple of thousands, but built up a vast private para-military terror organization staffed by mercenary soldiers called "Skullmen". Using a combination of high-level computer hacking and corrupt government officials on his payroll, he destroyed all records of his own past and assumed the mysterious phantom identity of... Dr X.
Meanwhile, Matthew was finally able to recall the circumstances surrounding his parents' death in vivid detail -- and realize that it was not an accident caused by him, but murder at the hands of his brother. He returned to the Western world with extraordinary mental and physical skills and an obsessive personal mission. He knew he must bring to justice the killer of his parents (and avenge his own years of suffering the guilt of thinking he had killed them). And at the same time, he must protect the world from his brother. For the sheer force of evil of Dr. X was known no better to anyone than to his younger brother Matthew -- now fully aware of the psychopathic depths to which his brother was capable of sinking in his lust for power and control.
Lacking anything remotely approaching the resources and paramilitary organization of Dr. X, Matthew decided to destroy his brother from within by infiltrating his organization. After some time working undercover as a Skullman, Action Man is ready to take down Dr. X out. Shortly after this, Matthew is assigned to a mission with Dr. X and his Skullmen, but on the mission they cross paths with the Action Force. So on that fateful night at the chalet in Switzerland. Matthew blew his cover (and everything that he had worked for) to save the innocent lives of Action Force. The result was the explosive concussion, combined with traces of Dr. X's psychotropic drugs, which caused him to lose his memory -- including his vast knowledge of Dr. X's empire, Dr. X's own personal past and Matthew's shocking relationship to Dr. X.
Meanwhile, Dr. X learned the true identity of the infiltrator who knew so dangerously much about his organization, who came so close to taking Dr. X's entire empire down. He also learned that this infiltrator (his brother) now has amnesia. This means that all the information so dangerous to Dr. X is locked away (for the moment irretrievably) in 's concussed brain.
In order to try to ensure that Matthew's memory does not return, Dr. X has used his extensive technological resources and worldwide network of corrupt officials to erase any trace of his brother's personal history and identity. Just as the person known as Dorian Exler disappeared from all private and public written records, it's now as if Matthew Exler never existed either...
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