Saint Augustine (November 13, 354 - August 28, 430) in Algeria, Bishop of Hippo, was a philosopher and theologian. Augustine, a Latin Father and Doctor of the Church, is one of the most important figures in the development of Western Christianity. Augustine was radically influenced by Platonism. Cross, F. L., ed. The Oxford dictionary of the Christian church. New York: Oxford University Press. 2005 He framed the concepts of original sin and just war. When Rome fell and the faith of many Christians was shaken, Augustine developed the concept of the Church as a spiritual City of God, distinct from the material City of Man. Durant, Will. Caesar and Christ. New York: Simon and Schuster. 1972 Augustine's work defined the start of the medieval worldview, an outlook that would later be firmly established by Gregory the Great. Durant, Will. Caesar and Christ. New York: Simon and Schuster. 1972

Augustine was born in present day Algeria to a Christian mother, Saint Monica. He was educated in North Africa and resisted his mother's pleas to become Christian. He lived as a pagan intellectual, took a concubine, and became a Manichean. He later converted to Christianity, became a bishop, and opposed heresies, such as the belief that people can deserve salvation by being good (Pelagianism). His works—including The Confessions, which is often called the first Western autobiography—are still read around the world. In addition he believed in Papal supremacy.

In Roman Catholicism and the Anglican Communion, he is a saint and pre-eminent Doctor of the Church, and the patron of the Augustinian religious order. Many Protestants, especially Calvinists, consider him to be one of the theological fathers of Reformation teaching on salvation and grace. In the Eastern Orthodox Church he is a saint, and his feast day is celebrated annually on June 15, though a minority are of the opinion that he is a heretic, primarily because of his statements concerning what became known as the filioque clause. Among the Orthodox he is called Blessed Augustine, or St. Augustine the Blessed. "Blessed" here does not mean that he is less than a saint, but is a title bestowed upon him as a sign of respect. The Orthodox do not remember Augustine so much for his theological speculations as for his writings on spirituality.