Augustine of Hippo, also known as St. Augustine, St. Austin, was bishop of Hippo Regius (present-day Annaba, Algeria). He was a Latin philosopher and theologian from the Africa Province of the Roman Empire and is generally considered as one of the greatest Christian thinkers of all times. His writings were very influential in the development of Western Christianity. According to his contemporary Jerome, Augustine established anew the ancient Faith. In his early years he was heavily influenced by Manichaeism and afterward by the Neo-Platonism of Plotinus. After his conversion to Christianity and his baptism in 387, Augustine developed his own approach to philosophy and theology, accommodating a variety of methods and different perspectives.
He believed that the grace of Christ was indispensable to human freedom, and he framed the concepts of original sin and just war. When the Western Roman Empire was starting to disintegrate, Augustine developed the concept of the Catholic Church as a spiritual City of God (in a book of the same name), distinct from the material Earthly City.
His thoughts profoundly influenced the medieval worldview. Augustines City of God was closely identified with the Church, the community that worshiped the Trinity. In the Catholic Church and the Anglican Communion, he is a saint and pre-eminent Doctor of the Church. Many Protestants, especially Calvinists, consider him to be one of the theological fathers of the Protestant Reformation due to his teaching on salvation and divine grace.
In the Eastern Orthodox Church he is also considered a saint. He carries the additional title of Blessed. Among the Orthodox, he is called Blessed Augustine or St. Augustine the Blessed