DIDYMUS, of Alexandria, an ecclesiastical writer who flourished in the fourth century. Notwithstanding his blindness, which took place before he had learned to read, he succeeded in mastering the whole circle of the sciences then known; and on entering the service of the church he was placed at the head of the Alexandrian theological school. Most of his theological works are lost. We possess however a Latin translation by Jerome of his Treatise on the Holy Ghost, and a similar translation by Epiphanius of his Brief Comments on the Canonical Epistles. A Treatise against the Manichæans is extant in the original Greek, and was first published at Bologna in 1796.