Aurelius Augustinus (AD 354-430), bishop of Hippo in Roman North Africa. Born to a Christian mother (Monica) and pagan father, he spent his twenties in the Manichaean sect and in academic rhetoric before his conversion in AD 386 (Milan, age 32), famously sparked by hearing a child's voice chant "tolle lege" — "take up and read" — leading him to Romans 13:13-14. Ordained bishop in AD 395, he wrote for the next 35 years. Chief works: Confessions (autobiography as prayer), City of God (the fall of Rome and the two cities), On the Trinity, and the massive anti-Pelagian corpus.
Augustine is the most influential Christian theologian after Paul, and the fountainhead of Western theology — both Roman Catholic and Protestant. Four areas where he stamped the Church: (1) Original sin — he systematized the doctrine that Adam's guilt and corruption are inherited by all his descendants; (2) Grace — against Pelagius, he insisted salvation is entirely God's initiative, not a cooperation rewarded for human effort; (3) Predestination — he taught unconditional election, a position later carried forward by the Reformers; (4) The Church and the two cities — the City of God (those ordered by love of God) and the City of Man (those ordered by love of self) run through all of history. Luther was an Augustinian monk; Calvin quoted Augustine more than any other theologian. The Reformation was largely a dispute over which Augustine (his doctrine of grace or his doctrine of the Church) took priority. His Confessions — "our heart is restless until it rests in Thee" — remains the most piercing spiritual autobiography ever written.