The prominent theologian best known for his influential writings on Christian doctrine is Augustine of Hippo. Living in the late 4th to early 5th centuries, Augustine's works, particularly *Confessions* and *City of God*, profoundly shaped Western Christian thought. His concepts, such as original sin, grace, and the nature of God, remain essential in both Catholic and Protestant theology. He integrated philosophical ideas, particularly Platonic thought, into Christian doctrine, making theology more accessible and intellectually robust. Augustine's impact on Christianity and philosophy endures, influencing countless theologians and philosophers throughout history.