Augustine of Hippo (13 November 354 – 28 August 430 AD) was a Roman African, Manichaean, early Christian theologian, doctor of the Church, and Neoplatonic philosopher from Numidia. He was the bishop of Hippo Regius in North Africa and is viewed as one of the most important Church Fathers of the Latin Church for his writings in the Patristic Period. Among his most important works are The City of God, De doctrina Christiana, and Confessions.
According to his contemporary, Jerome, Augustine “established anew the ancient Faith”. In his youth he was drawn to Manichaeism and later to neoplatonism. After his baptism and conversion to Christianity in 386, 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 imagined the 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 On the Trinity.