Dionysius of Alexandria, surnamed "the Great," was a third-century bishop of Alexandria whom the Church remembers as a teacher, a confessor under persecution, and a guide through several of the doctrinal and disciplinary crises of his age. Born around 190 to a wealthy pagan family of the city, he converted to Christianity as an adult and entered the Catechetical School of Alexandria, where he studied under Origen. He rose to lead that school and, around 248, was raised to the episcopal throne of Alexandria, which he held until his death.
His tenure spanned the imperial persecutions under Decius and Valerian, during which he was hunted, captured, and exiled, yet survived to continue governing his church. Later writers, including Eusebius of Caesarea and Basil the Great, honored him with the title "the Great." The Orthodox calendar commemorates him as a hieromartyr on October 5.