Ildephonsus was educated at Seville under St. Isidore — the last of the great Spanish Latin Fathers — and entered the Benedictine monastery of Agali near Toledo as a young man. Elected archbishop of Toledo in 657, he ruled the Spanish primatial see for ten years.
His treatise De Virginitate Perpetua Sanctae Mariae ('On the Perpetual Virginity of Holy Mary') is the most extensive Marian theological work of the early medieval West and the foundation of Spanish Marian devotion. Tradition holds that the Blessed Virgin appeared to him in person, descending into his cathedral on December 18, 665, and vested him with a chasuble of heavenly wool as a sign of her favor — the iconographic origin of the Spanish 'imposition of the chasuble' theme depicted by El Greco, Murillo, and countless others.
He died on January 23, 667; his feast is observed in Spain and Spanish America with great solemnity, and the Cathedral of Toledo, which he served, remains the primatial see of the Iberian peninsula.