According to what I've read, the candidate considered most likely to be the man in the iron mask is Nicolas Fouquet, Louis XIV's finance minister. It's reasonable to assume that Fouquet was involved in the machinations of a secret society and that, somehow, Louis Catorce found out and had him imprisoned. The king also went to great trouble to obtain Poussin's painting "Les Bergers d'Arcadie" which he kept isolated from view in his private rooms.

King Louis tried his best to get the courts to sentence Fouquet to death, but the members of the secret society managed to influence public opinion and the judges to give him life. So Louis kept him in solitary confinement with no opportunity to communicate with anyone at all.

ananda