Augustine of Hippo, also known as Saint Augustine or Saint Austin, was an early Christian theologian and philosopher whose writings influenced the development of Western Christianity and Western philosophy. He was the bishop of Hippo Regius (modern-day Annaba, Algeria), located in Numidia (Roman province of Africa). He is viewed as one of the most important Church Fathers in the Western Christianity for his writings in the Patristic Era. Among his most important works are City of God and Confessions.
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 baptism and conversion to Christianity in 387, Augustine developed his own approach to philosophy and theology, accommodating a variety of methods and perspectives. Believing that the grace of Christ was indispensable to human freedom, he helped formulate the doctrine of original sin and made seminal contributions to the development of just war theory.
When the Western Roman Empire began to disintegrate, Augustine developed the concept of the Catholic Church as a spiritual City of God, distinct from the material Earthly City. His thoughts profoundly influenced the medieval worldview. The segment of the Church that adhered to the concept of the Trinity as defined by the Council of Nicaea and the Council of Constantinople closely identified with Augustine's City of God.
In the Catholic Church and the Anglican Communion, he is a saint, a pre-eminent Doctor of the Church, and the patron of the Augustinians. His memorial is celebrated on 28 August, the day of his death. He is the patron saint of brewers, printers, theologians, the alleviation of sore eyes, and a number of cities and dioceses. Many Protestants, especially Calvinists, consider him to be one of the theological fathers of the Protestant Reformation due to his teachings on salvation and divine grace.
In the East, many of his teachings are not accepted. The most important doctrinal controversy surrounding his name is the filioque. Other possibly unacceptable doctrines include his views on original sin, the doctrine of grace, and predestination. Nonetheless, though considered to be mistaken on some points, he is still considered a saint, and his feast day is celebrated on 15 June. He carries the additional title of Blessed as opposed to Saint among the Orthodox Church, due to his teachings controversial with the doctrine.