Leo the Great

Leo the Great (c. 400–461), pope from 440, defended both the unity of the church and the integrity of the faith. His Tome supplied the decisive language of the Council of Chalcedon (451) on the two natures of Christ in one person. A vigorous preacher and a Doctor of the Church.

Leo's Tome (449) gave the church its classic statement that the one Christ exists in two complete natures, divine and human, without confusion or division — language the Council of Chalcedon adopted as the standard of orthodoxy. A great preacher, his sermons on the seasons of the church year expound the mysteries of Christ's life with clarity and warmth, and his firm leadership greatly strengthened the teaching authority of the Roman see.