A Saint and patriarch. He was the 33rd patriarch of Alexandria (535-566). He is commemorated on the 28th of Baounah. He was a devoted friend and of Severus of Antioch. Riots of the followed his consecration. He was able to exercise his authority only briefly but later was forced to go to Constantinople, where he became a symbol of orthodoxy. He acquired such an excellent reputation that the non-Chalcedonians were called “Theodosians” after his name for a long time.

Information concerning his life has survived in Coptic sources. Theodosius wrote a lengthy homily on the Baptist, giving details on the life of the forerunner of Christ. He also wrote a homily on the Archangel Michael, and a third homily on the Virgin Mary that is currently in the Vatican Library. In this homily, he describes the virtues of the Virgin Mary, partially published by Robinson; there is a letter ascribed also to him.