John of Damascus (d. 749), was a theologian of the early church. He was convinced that Islam was not a new religion, but a variation on the Judaeo-Christian faith. This view is interesting because John grew up as a young Arab aristocrat in the Ummayad Court at Damascus, which was the center of the Islamic world of his day. His father was a Christian and the Chancellor of the government. John was a boyhood friend of the future Caliph al-Yazid, and the two boys' drinking and fighting in the streets of Damascus were a major topic of conversation.

When John grew older, he moved to the desert monastery of Mar Saba where he began work on his greatest work The Fount of Knowledge. The book contains a detailed critique of Islam - the first ever written by a Christian. John viewed Islam as a heretical form of Christianity closely related to the heretical doctrine of Arianism. Both believe that God could not become fully human because this would compromise His divinity.