The Abbé Étienne Guibourg was a French Roman Catholic abbé and occultist who was involved in the affaire des poisons, during the reign of Louis XIV. He has been variously described as a "defrocked" or "renegade" priest, and is said to have also had a good knowledge of chemistry. He is best known for performing a series of Black Mass rituals with Catherine Monvoisin for Madame de Montespan.
Guibourg performing his Black Mass with the naked body of Madame de Montespan for an altar, as depicted in The Guibourg Mass by Henry de Malvost, Paris, 1903.