Saint John Damascene (b. circa 675, died 749) was a Syrian Christian that lived under Muslim rule all of his life. St. John wrote the first comprehensive compilation of Christian theology. John defended the Church’s understanding for the veneration of images and he was known as a fierce opposer of iconoclasts. John was dedicated to a life of prayer who guarded the Church's faith and traditions zealously. He had an extraordinary devotion to the Mary, Mother of God. In 1890, Pope Leo XIII proclaimed John Damascene Doctor of the Church.
Nothing is known of John's mother. Born in Damascus, John was baptized immediately on his birth.  He lived at the time when Syria fell into the hands of the Arabs. John's father was a faithful Christian, a wealthy man of honorable rank that commanded the respect of the Arab conqueror, and were employed in judicial offices of trust and dignity as an administrator of Christian law to the Christian subjects of the Sultan. John's father was devoted to the redemption of Christian slaves. Saracen pirates swept the Mediterranean and brought in Christian captives from all quarters. An Italian monk named Cosmas had the misfortune to fall into the hands of Saracens. The father of John, thought he would make a valuable tutor for his son. Thanks to John's father, his life was spared by the Saracen governor and placed his son under his guidance.  Under the tutelage of Cosmas, John made such rapid progress that he soon equalled Diophantus in algebra and Euclid in geometry. Equal progress was made in music, astronomy, and theology. On the death of his father, John Damascene was given a government position, chief councillor of Damascus.
In 726, Leo the Isaurian of the Eastern Church, issued his first edict against the veneration of images. John oppose the Byzantine monarch and he also stirred the people to resistance. In 730, a more stringent edict on icons was enforced. John Damascene replied with even greater vigour than before. He wrote a letter to the Byzantine emperor and warned to beware of the consequences of this unlawful action, which stoked the anger of the emperor. The Sultan received a forged letter of John, sent from emperor Leo, writing the crime of betraying the city of Damascus. The Sultan ordered the authors hand to be severed at the wrist. The sentence was executed, but through the intervention of the Blessed Virgin, the amputated hand was miraculously restored. John Damascene heard the calling to a higher life, resigned his official government position and went to the monastery of St. Sabas, eight miles southeast of Jerusalem. After a probationary period, John V, Patriarch of Jerusalem, made him a priest. In 754, the successor of Leo, Constantine Copronymus, reconfirmed the principles of the Iconoclasts and cursed by name those who had opposed them. John was singled out as he was called a "cursed favourer of Saracens", a "traitorous worshipper of images", a "wronger of Jesus Christ", a "teacher of impiety", and a "bad interpreter of the Scriptures". At the emperor's command, his name was written "Manzer" (a bastard).  But the Seventh General Council of Nicea (787) made ample amends for the insults of his enemies and he was surnamed Chrysorrhoas (golden stream).
John is regarded as the first Scholastic, and his "De fide orthodoxa" as the first work of Scholasticism. The most important and best known of all his works is called "Fountain of Wisdom." It is said that this book is to Eastern schools what the Summa of Aquinas became to the West. The "Fountain of Wisdom" is divided into three parts, namely, "Philosophical Chapters", "Concerning Heresy", and "An Exact Exposition of the Orthodox Faith." It is largely a summary of the Categories of Aristotle. The purpose to give his readers only such philosophical knowledge as was necessary for understanding. It is a record of the technical terminology used by the Greek Fathers, not only against the heretics, but also in the exposition of the Faith for the benefit of Christians. The first book of "The Orthodox Faith" treats of the essence and existence of God, the Divine nature, and the Trinity. The second books' chapters were devoted to Islam, Iconoclasm, Aposchitae and lists eighty heresies. He added twenty heresies that had sprung up since his time. In treating of Islam, he assails the immoral practices of Mohammad and the corrupt teachings inserted in the Koran. "Concerning the Orthodox Faith", the third book of the "Fountain of Wisdom", is the most important of John Damascene's writings and one of the most notable works of Christianity. The collection of a single work, collected the theological opinions of the ancient writers scattered through many volumes, and of systematizing them in a logical whole in the modern day eighth century. Under the general title of "Homilies" he wrote fourteen discourses. These sermons concern Transfiguration, Assumption, Nativity, Epiphany, and Pentecost, Epistles to the Ephesians, Philippians, Colossians, Thessalonians and others. The most famous of the "canons" is that on Easter, which contains the liturgical hymns used by the Greek Church in its Sunday services. John adapted choral music to the purposes of the Liturgy.
Little is known of John's death. It is believed he died in Jerusalem. His eloquent defense of images has earned him the title of "The Doctor of Christian Art." He is also known as the last great Father of the Eastern Church.
"The saints must be honored as friends of Christ and children and heirs of God,'But as many as received him, he gave them the power to be made the sons of God....' Let us carefully observe the manner of life of all the apostles, martyrs, ascetics and just men who announced the coming of the Lord. And let us emulate their faith, charity, hope, zeal, life, patience under suffering, and perseverance unto death, so that we may also share their crowns of glory."
- [http://www.catholic.org/saints/saint.php?saint_id=66 St. John of Damascus] Catholic Online
- St. John of Damascus Catholic Online
- St. John Damascene Catholic Encyclopedia