The Man in the Iron Mask is the final part of Alexander Dumas' The Vicomte de Bragelonne, which follows from The Three Musketeers and Twenty Years After. Few people know that the man in the iron mask actually existed.
"The Man in the Iron Mask (French: L'Homme au Masque de Fer) (died November 1703) was a prisoner who was held in a number of jails, including the Bastille and the Chateau d'If, during the reign of Louis XIV of France. The identity of this man has been thoroughly discussed, mainly because no one ever saw his face which was hidden by a mask of black velvet cloth. Later retellings of the story have claimed that it was an iron mask.
In popular myth he is believed to have been the twin brother of Louis XIV, but there is little actual evidence for this.
What facts are known about this prisoner are based mainly on correspondence between his jailer and his superiors in Paris."