During the reign of King Louis XIV, an enigmatic man spent several decades confined to the Bastille and other French prisons. No one knew his identity or why he was in jail. Even stranger, no one knew what he looked like—the prisoner was never seen without a black velvet mask covering his face.

The anonymous prisoner has since inspired countless stories and legends—writings by Voltaire and Alexandre Dumas helped popularized the myth that his mask was made of iron—yet most historians agree that he existed. So who was he?

Hundreds of different candidates have been proposed ranging from a member of the royal family to a disgraced French general and even the playwright Molière. Still, evidence indicates that only two prisoners were in custody during the same timeframe as the “Mask”: Ercole Matthiole and Eustache Dauger.

Matthiole was an Italian count who was abducted and jailed after he tried to double-cross Louis XIV during political negotiations in the late-1670s. He was a longtime prisoner, and his name is similar to “Marchioly”—the alias under which the Mask was buried. Even more convincing is that Louis XV and Louis XVI both supposedly said the Mask was an Italian nobleman.

Unfortunately, Matthiole likely died in 1694—several years too early for him to be the Mask. With this in mind, many to point to the enigmatic Eustache Dauger as the more likely culprit. His 1669 arrest warrant included a letter from a royal minister instructing jailers to restrict his contact with others and to “threaten him with death if he speaks one word except about his actual needs.” Dauger was frequently shepherded between several prisons, and once was transported in a covered chair so that passersby would not see his face.

While Dauger is a popular candidate for being the Mask, historians still don’t know who he was or if his name was a pseudonym. One theory holds that he was a lowly valet implicated in a political scandal, but he’s also been identified as a debauched nobleman, a failed assassin and even the twin brother of Louis XIV.