St. Anselm was an Italian Benedictine monk, philosopher, and theologian who lived in the 11th century. He is best known for his ontological argument for the existence of God, which is a key contribution to the philosophy of religion. Anselm also served as the Archbishop of Canterbury and played a significant role in the Investiture Controversy, a power struggle between the church and the state. He is considered a Doctor of the Church and is honored as a saint in the Catholic Church and the Anglican Communion.