St. Illtud (also spelled Illtyd, Eltut, and, in Latin, Hildutus), also known as Illtud Farchog "Illtud the Knight", is venerated as the founder-abbot and teacher of the divinity school known as Cor Tewdws, located in Llanilltud Fawr (Llantwit Major) in the Welsh county of Glamorgan. He founded the monastery and college in the 6th century, and the school is believed to be Britain’s earliest centre of learning. At its height, it had over 1000 pupils and schooled many of the great saints of the age, including Saint Patrick of Ireland, Saint David of Wales, Gildas the Historian, and Samson of Dol.
St. Illtud was popular among the very ancient Celts, but there are few dependable sources about his life story. The earliest mention of St. Illtud is in the Vita Sancti Sampsonis, written in Dol, Brittany, about 600 AD. According to this account, Illtud was the disciple of Bishop Germanus of Auxerre in north-central France. According to the St. Sampson biography, Illtud was the most accomplished of all the Britons, and was well versed in the scriptures of the Old and New Testaments, as well as every type of philosophy, including geometry, rhetoric, grammar, and arithmetic. He was also "gifted with the power of foretelling future events". It appears that he was an educated Briton living shortly after Rome's departure from the West.