German monk and theologian (1483-1546), Augustinian friar and professor of biblical theology at Wittenberg. On October 31, 1517, he posted 95 theses against the sale of indulgences on the door of the Castle Church in Wittenberg — conventionally reckoned the start of the Protestant Reformation. Excommunicated in 1521, he stood before the Diet of Worms that same year and (per tradition) declared, "Here I stand, I can do no other. God help me. Amen." His translation of the Bible into German gave the Reformation its rocket fuel: ordinary Christians reading ordinary Scripture in ordinary language, for the first time in centuries.
Luther is the Reformation's battering ram. Five doctrinal hammer-blows reshape Christianity under his influence: (1) Sola Scriptura — Scripture alone is the final authority, not popes or councils; (2) Sola Fide — justification is by faith alone, not faith + works or faith + sacraments; (3) Sola Gratia — salvation is by grace alone; (4) Solus Christus — Christ alone is Mediator, making priestly mediation unnecessary; (5) Soli Deo Gloria — glory to God alone, not to saints, Mary, or hierarchy. His Small Catechism and Large Catechism still shape Lutheran teaching worldwide. His "two kingdoms" doctrine shaped Protestant political theology. His hymns — especially "A Mighty Fortress Is Our God" — became the battle songs of the Reformation. Like all reformers he had feet of clay: his later anti-Jewish writings were ugly, ready ammunition for the Nazi regime four centuries later, a sobering reminder that theological brilliance does not guarantee personal sanctification. But the gospel he recovered is the gospel by which the Church still lives.