Pope Demetrius of Alexandria was Patriarch of Alexandria (189–232). Sextus Julius Africanus, who visited Alexandria in the time of Demetrius, places his accession as eleventh bishop after Mark in the tenth year of Commodus; Eusebius of Caesarea's statement that it was in the tenth of Septimius Severus is a mistake.
The Catholic Encyclopedia states, "Demetrius is the first Alexandrian bishop of whom anything is known." While Jerome claimed that Demetrius sent Pantaenus on a mission to India, it is likely that Clement had succeeded Pantaenus as the head of the Catechetical School before the accession of Demetrius. When Clement retired (c. 203), Demetrius appointed Origen, who was in his eighteenth year, as Clement's successor.
While Demetrius was a scholar in his own right, taking part in the controversy over the proper calculation of Easter that preoccupied the Church in the time of Pope Victor I, Origen's brilliance eventually outshone Demetrius, and it is in his relationship with the famous theologian that Demetrius is defined in history.
Demetrius gave Origen encouragement at the beginning of his career, and is said to have shown him favor. He dispatched Origen to the governor of Arabia, who had requested his presence in letters to the prefect of Egypt as well as to Demetrius. When the Emperor Caracalla sacked Alexandria (215) in punishment for their satire directed at him, Origen fled to Caesarea, where the bishops present requested that he give sermons. Demetrius wrote to him a rebuke that this activity was not fitting for a layman. Bishops Alexander of Jerusalem and Theoctistus of Caesarea wrote in his defense and mentioned precedents for laymen to give sermons, but despite their efforts Demetrius recalled Origen. Once Origen was back in Alexandria, the strain in their relationship eased.
In 230 Origen was asked to settle a dispute in Achaea which required his presence, so he set out by way of Palestine, perhaps without the permission of Demetrius. Moreover, Origen was ordained priest at Caesarea without leave. When Demetrius learned of this, he considered it an act of insubordination, which ended their relationship. Demetrius convened a synod in 232 that banished Origen, then sent a formal condemnation of Origen to all the churches. Rome accepted the decision, but Palestine, Phoenicia, Arabia, Achaea rejected it. From Caesarea Origen sent forth letters in his own defence, and attacked Demetrius.
Demetrius put the Catechetical School under the charge of Heraclas, the first pupil of Origen, who had long been his assistant. This may have been Demetrius' final act as bishop.