Church History by Eusebius Pamphilius
Chapter XXX.--The Pupils of Origen.
While Origen was carrying on his customary duties in Cæsarea, many pupils came to him not only from the vicinity, but also from other countries. Among these Theodorus, the same that was distinguished among the bishops of our day under the name of Gregory, and his brother Athenodorus, we know to have been especially celebrated. Finding them deeply interested in Greek and Roman learning, he infused into them a love of philosophy, and led them to exchange their old zeal for the study of divinity. Remaining with him five years, they made such progress in divine things, that although they were still young, both of them were honored with a bishopric in the churches of Pontus.