Theophilus was a second-century Patriarch of Antioch. We gather from his writings (the only remaining being his apology to Autolycus) that he was born a pagan, not far from the Tigris and Euphrates, and was led to embrace Christianity by studying the Holy Scriptures, especially the prophetical books. He makes no reference to his office in his existing writings, nor is any other fact in his life recorded. Eusebius, however, speaks of the zeal which he and the other chief shepherds displayed in driving away the heretics who were attacking Christ's flock, with special mention of his work against Marcion.