Martin Luther (1483–1546) was the German monk and theologian whose protest against the Catholic Church led to the Protestant Reformation. On October 31, 1517, Luther presented ninety-five “theses,” or protests, on abuses of power in the church to Archbishop Albert of Mainz. The archbishop forwarded Luther’s “Theses on the Power of Indulgences” to Rome, and in 1518 Luther was summoned there to face charges of heresy. He was excommunicated by Pope Leo X and went into hiding, while his ideas about the church spread through Germany and beyond,...