Bénigne d'Auvergne de Saint-Mars was a French prison governor in the late 17th and early 18th century. He is best known as the apparent keeper of the Man in the Iron Mask.^[1] 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.^[2]

From 1665 to the spring of 1681, Saint-Mars was the Officer-in-Charge of the donjon (the main tower) of the fortress Pinerolo (in French Pignerol, 40 kilometers WSW of Turin, Italy), which then belonged to France. Saint-Mars acted as governor of the nearby fortified castle of Exilles from 1681.^[3]

In 1687, Saint-Mars became the governor of two islands, Île Sainte-Marguerite and Île Saint-Honorat, in the gulf of Cannes (these islands are now called the Lérins Islands) until 1698. At that time he became governor of the Bastille in Paris, a post he held until his death on 18 September 1708.^[4]