Augustine of Hippo, also known as St Augustine, St Austin, or St Augoustinos, was a Father of the Church whose writings are considered very influential in the development of Western Christianity and philosophy. He was bishop of Hippo Regius of the Roman province of Africa.
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 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. Augustine's City of God was closely identified with 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.