Bénigne d'Auvergne de Saint-Mars was a Frenchprison governor in the late 17th and early 18th century. He is best known as the apparent keeper of the Man in the Iron Mask. According to letters written by Saint-Mars to various officials and ministers of France, he had in his custody a prisoner of State, whom he carried with him from Pinerolo to the Lérins Islands, and later to the Bastille.
From 1665 to the spring of 1681 Saint-Mars was the Officer-in-Charge of the donjon (the main tower) of the fortress Pinerolo (present day Pignerol, 40 kilometers WSW of Turin, Italy), which then belonging to France. Saint-Mars acted as governor of the fortified castle Exiles from 1681.