Saint John (surnamed Mansur, later called Chrysorroas, "the Golden Stream" for his writing) was born in Damascus, Syria, late in the 7th century. (This was soon after the Umayyad dynasty took control of the region from the Eastern Roman Empire.) His parents were wealthy and pious Christians, and his father Sergius served the Caliph of Damascus. John was educated in philosophy, and his enlightenment impressed the Caliph.
Saint John defended the Holy Icons against the persecutions of Emperor Leo the Isaurian. As John was beyond his power, Leo forged a letter from John inviting Leo to attack Damascus. The Caliph was enraged and severed John's right hand, which was restored by the Theotokos. At this miracle, the Caliph restored John as his advisor.
The Saint wished to enter the monastic life, however, and after much pleading obtained the Caliph's permission. Saint John entered the Monastery of Saint Sabbas, where he concealed his worldly position. Later, at the insistence of the Theotokos, he began to write theological treatises and compose hymns.
He continued to defend the holy icons during the waves of iconoclasm, and was one of the first Christian theologians to refute the teachings of Islam. He was a prolific hymnographer, composing countless hymns which continue to be used in the Church today. He reposed in peace in 760, at the age of 84. His feast is celebrated on December 4.