Augustine of Hippo (November 13, 354 – August 28, 430), also known as Augustine, St. Augustine, St. Austin,  St. Augoustinos, Blessed Augustine, or St. Augustine the Blessed, was Bishop of Hippo Regius (present-day Annaba, Algeria). He was a Latin philosopher and theologian from Roman Africa. 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 baptism in AD 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.^[9] His thoughts profoundly influenced the medieval worldview. Augustine's City of God was closely identified with the Church, the community that worshipped God.

In the Catholic Church and the Anglican Communion, he is a saint and pre-eminent Doctor of the Church, and the patron of the Augustinian religious order; his memorial is celebrated 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.^[11] Many Protestants, especially Calvinists, consider him to be one of the theological fathers of the Reformation due to his teaching on salvation and divine grace. In the Eastern Orthodox Church he is also considered a saint, his feast day being celebrated on 15 June. He carries the additional title of Blessed. Among the Orthodox, he is called "Blessed Augustine", or "St. Augustine the Blessed".