Augustine: The Great Theologian:

Paul and Peter helped spread Christianity around the ancient world, but competing worldviews came along with it; Gnosticism and Neoplatonism. Christians needed a big brain to defend their worldview in the face of these challenges, and that brain was Saint Augustine. A recent convert, Augustine became known as "doctor of grace" as he shed light on reality, perception, and on how the truth that God provides points back to Him.