John of Damascus

John of Damascus — known before his monastic life, according to the traditions, as Mansur ibn Sarjun — was born around 675 CE in Damascus, into a long-established Arab Christian family of financial administrators: his grandfather Mansur ibn Sarjun managed the city's finances in the late Byzantine and early Umayyad periods, and his father Sarjun continued serving in the caliphs' bureaus. The standard account holds that John himself held an administrative post at the Umayyad court, though contemporary documentation of his life is scarce.

Around the beginning of the eighth century he left the administration and became a monk; a later tradition places him at the Monastery of Mar Saba in the Judaean Desert, a detail some modern scholars have questioned. He was ordained a priest by Patriarch John V of Jerusalem.

His best-known work, the "Fount of Knowledge," includes the "Exact Exposition of the Orthodox Faith" — the most influential systematic summary of Greek patristic theology — alongside three treatises in defence of the veneration of icons written amid the iconoclastic controversy; translated into Latin, his work later fed into Western scholastic theology.

He died around 749 CE — the synod of Hiereia in 754 condemned him as already deceased — though some scholars prefer a date between 750 and 753. He is venerated in both Eastern and Western churches, and the Vatican proclaimed him a Doctor of the Church in 1890.