Pierre Plantard de Saint-Clair (born Pierre Athanase Marie Plantard, 18 March 1920 – 3 February 2000) was a French draughtsman, best known for being the principal perpetrator of the Priory of Sion hoax, by which he claimed from the 1960s onwards that he was a direct and legitimate male line Merovingian descendant of Dagobert II and the "Great Monarch" prophesied by Nostradamus. Today in France he is commonly regarded as a mystificator.