Leo I, St, known as ‘ Leo the Great’ (d. 461). Pope from 440, who worked to enhance the pre-eminence of the see of Rome, claiming jurisdiction in Africa, Spain, and Gaul. Leo composed his Tome, expounding the Christology of the Latin Church, according to which Jesus Christ is one person, the divine Word, in whom are two unconfused natures, the divine and human; each of these exercises its own particular faculties, but because of the communicatio idiomatum it may be said that the Son of Man descended from heaven, and the Son of God was crucified. The Tome was given formal authority at the Council of Chalcedon in 451. Leo was declared a Doctor of the Church by Benedict XIV.

Leo I, Saint (390–461) (Leo the Great) Pope (440–61). He established important points of doctrine, including the dual nature of Christ, which he propounded at the Council of Chalcedon (449). By personal meetings, he saved Rome from Attila (452) and the Vandal leader Gaiseric (455).