Saint Proclus, Archbishop of Constantinople, from his early years devoted all his time to prayer and the study of Holy Scripture. The Lord granted him the great good fortune to be a disciple of Saint John Chrysostom (November 13), who at first ordained him as a deacon, and then to the holy priesthood. He witnessed the appearance of the Apostle Paul to Saint John Chrysostom. Saint Proclus received from his teacher a profound understanding of Holy Scripture, and learned to elucidate his thoughts in a polished form.

After the exile and death of Saint John Chrysostom, the holy Patriarch of Constantinople Sisinius (426-427) consecrated Saint Proclus as bishop of the city of Kyzikos, but under the influence of Nestorian heretics he was expelled by his flock there…

Excerpt from the OCA official website, links to full article and various writings on the Theotokos below…