Lucas de Tui (or O Tudense) (died 1249) was a Leonese cleric and intellectual, remembered best as a historian. He was Bishop of Tuy from 1239 until his death. Born in León, Lucas was a canon of San Isidoro there between 1221 and 1239. While a canon he wrote De Miraculis Sancti Isidori in defence of Isidore of Seville. He also travelled extensively: to Rome, Constantinople, Cyprus, Jerusalem, Armenia, and France. He visited all four of the Holy Nails: in France, Constantinople, Nazareth, and Tarsus. In 1233 or 1234 he passed Easter in Rome and completed his tract De altera vita fideique controversiis adverus Albigensium errores against the Cathars, taking inspiration mainly from Isidore and Jerome.