John of Damascus was the last of the great Greek Fathers — a systematic theologian, defender of icons, and liturgical poet whose Exact Exposition of the Orthodox Faith became the standard textbook of Eastern theology and deeply influenced the Western scholastics. Writing from the safety of the monastery of Mar Saba in Palestine (then under Islamic rule, beyond the reach of the iconoclast emperors), he provided the definitive theological defense of the veneration of images and produced a comprehensive synthesis of Greek patristic thought.

A later hagiographic tradition (preserved in a 10th-century vita) claims that the Caliph, deceived by a forged letter, had John's right hand cut off for treason, but that the hand was miraculously restored through the intercession of the Virgin Mary. This story generated the iconographic tradition of the 'Three-Handed Theotokos' (Trojeručica), venerated particularly in Serbian Orthodoxy.

The story has no early attestation and is absent from John's own writings and from Theophanes. It serves the theological point that the hand which defended icons was divinely preserved — a narrative too perfectly fitted to its purpose to inspire confidence.

John was born around 676 into a prominent Christian Arab family in Damascus. His father Sergius (Arabic: Mansur ibn Sarjun) served as a senior financial official under the Umayyad caliphate — the family had held administrative posts under both the Byzantine and Islamic governments. John received an excellent education, reportedly studying alongside the future Caliph Yazid I.

Around 706, John resigned his administrative position and entered the monastery of Mar Saba, near Jerusalem, where he was ordained priest. For the remaining four decades of his life he devoted himself to theological writing, liturgical composition, and the defense of orthodoxy.

His masterwork is the Fountain of Knowledge (Pege Gnoseos), a three-part theological encyclopedia: the Dialectica (a philosophical introduction drawing on Aristotle and the Neoplatonists), the De Haeresibus (a catalogue of heresies), and the De Fide Orthodoxa (Exact Exposition of the Orthodox Faith). The latter is a systematic presentation of Christian doctrine organized into 100 chapters, drawing on the full tradition of Greek patristic thought — Basil, Gregory, Chrysostom, Maximus, and above all the Cappadocians. It became the standard Eastern theological textbook and, through Peter Lombard's use of it, influenced Western scholasticism as well.

• Doctor
• Priest
• Monastic
• Hymn-Writer