Saint Cadoc or Cadog (; also ; born or before) was a 5th-6th century Abbot of Llancarfan, near Cowbridge in Glamorganshire, South Wales, a monastery famous from the era of the British church as a centre of learning, where Illtud spent the first period of his religious life under Cadoc's tutelage. Cadoc is credited with the establishment of many churches in Cornwall, Brittany Dyfed and Scotland. He is known as Cattwg Ddoeth, "the Wise", and a large collection of his maxims and moral sayings were included in Volume III of the Myvyrian Archaiology. He is listed in the 2004 edition of the Roman Martyrology under 21 September. His Norman-era "Life" is a hagiography of importance to the case for the historicity of Arthur as one of seven saints' lives that mention Arthur independently of Geoffrey of Monmouth's Historia Regum Britanniae.