is today. There is information on him here.
There has been a time in the history of Christianity, when it had been Athanasius against the world, and the world against Athanasius. The need and straitness of the Church had been great, and one man was raised up for her deliverance. In this second necessity, who was the destined champion of her who cannot fail? Whence did he come, and what was his name? He came with an augury of victory upon him, which even Athanasius could not show; it was Leo, Bishop of Rome.
Leo's augury of success, which even Athanasius had not, was this, that he was seated in the chair of St. Peter and the heir of his prerogatives. In the very beginning of the controversy, St. Peter Chrysologus had urged this grave consideration upon Eutyches himself, in words which have already been cited: "I exhort you, my venerable brother," he had said, "to submit yourself in everything to what has been written by the blessed Pope of Rome; for St. Peter, who lives and presides in his own See, gives the true faith to those who seek it." This voice had come from Ravenna, and now after the Latrocinium it was echoed back from the depths of Syria by the learned Theodoret. "That all-holy See," he says in a letter to one of the Pope's Legates, "has the office of heading ([hegemonian]) the whole world's Churches for many reasons; and above all others, because it has remained free of the communion of heretical taint, and no one of heterodox sentiments hath sat in it, but it hath preserved the Apostolic grace unsullied." And a third testimony in encouragement of the faithful at the same dark moment issued from the Imperial court of the West. "We are bound," says Valentinian to the Emperor of the East, "to preserve inviolate in our times the prerogative of particular reverence to the blessed Apostle Peter; that the most blessed Bishop of Rome, to whom Antiquity assigned the priesthood over all ([kata panton]) may have place and opportunity of judging concerning the faith and the priests." Nor had Leo himself been wanting at the same time in "the confidence" he had "obtained from the most blessed Peter and head of the Apostles, that he had authority to defend the truth for the peace of the Church." Thus Leo introduces us to the Council of Chalcedon, by which he rescued the East from a grave heresy.
Venerable John Henry Newman, C.O., An Essay on the Development of Christian Doctrine