Answer: A disloyal military officer
For centuries, people have been fascinated by the history of man in the United States iron mask. A mysterious prisoner who was in the fortress of Pignerol and was imprisoned by King Louis XIV at the end of the 1
Although we can not say with absolute certainty who the man was in the iron mask, we have very strong evidence that the man is a disloyal military officer. In the 19th century, French military cryptanalyst Etienne Bazeries took on the task of decrypting the "Big Cipher" of Louis XIV., A cryptographic code used by the king consisting of some 600 unique numbers. Despite the number going far beyond the number of letters in the French alphabet, Bazeries managed to almost completely crack the cipher by decrypting pairs of letters (of which there are 676 possible pairs in the French alphabet).
He opened a wealth of information about the then king and the country, including a letter from the king about the fate of a French military officer, Vivien de Bulonde. Bulonde had been responsible for a battle on the Italian border, but when he heard that his position was in danger, they fled (leaving his wounded men and supplies behind). King Louis was furious with the incident and ordered Bulonde to be imprisoned in the fortress of Pignerol, where he was kept under lock and key, and during the day only allowed to cross the battlements.
That something remains unknown because the pair of numbers indicating with which exactly Bulonde was allowed to commit the battlements is described by a pairing of numbers that occurs only once in the entire correspondence of the king and for the no comparison instance is likely never decrypted. Given that the man in the iron mask was emerging from Bulonde's cowardly desertion, Bazeries' cryptographic work provides the strongest evidence of the Iron Man's identity.