Illtud was a 6th-century Welsh abbot and teacher who established a significant monastery and divinity school in Llantwit Major. Recognized as a major figure in early Celtic Christianity, he founded what is considered one of the first major centers of learning in Britain. His school attracted many prominent scholars and saints, including David, Gildas, and Samson of Dol. While some traditions link him to a military past as a knight, he is primarily remembered for his profound influence on the religious and intellectual landscape of Sub-Roman Wales.