Bernard Gui (French: [ɡi]; 1261 or 1262 – 30 December 1331), born Bernard Guidoni, also known as Bernardo Gui or Bernardus Guidonis, was a French inquisitor of the Dominican Order in the Late Middle Ages during the Medieval Inquisition, Bishop of Lodève, and one of the most prolific writers of the Middle Ages. He is known for his tenure as Inquisitor of Toulouse against the Albigenses at the behest of Pope Clement V and Pope John XXII between 1307 and 1323.
He was born at Royères, in the Limousin, in 1261.
He entered the Dominican Convent at Limoges, and made his profession in 1280. Ten Years later he was made Prior of Albi, and subsequently at Carcassonne, at Castres, and at Limoges.
Working in the area of Toulouse (in modern France), his inquisition of those examined as suspected, known, reputed, or accused of the crime of heresy or support to heretics, led to over 900 guilty verdicts in fifteen years of office. People convicted of heresy during the time of the Inquisition were turned over to the secular arm (nobles and city leaders) for punishment. Out of all those convicted during examination by Gui, 42 were executed. The four sects of Christian heretics Gui wrote about in his Inquisitor’s Guide were the Manicheans, the Waldensians, the False Apostles, and the Beguines. Other groups which were not considered Christian but were cited in Gui’s Inquisitor’s Guide as “treacherous” were Jews, as well as Sorcerers, Fortune-tellers, and those who summon demons.