Martin Luther (1483 – 1546) was a German monk and theologian whose radical ideas sparked the Protestant Reformation in the 16th century. Frustrated by perceived corruption in the Catholic Church, particularly the selling of indulgences, he famously nailed his "Ninety-five Theses" to a church door in 1517. Luther championed salvation through faith alone, not good works, and the supreme authority of the Bible over church tradition. His defiance against the Pope and Emperor fundamentally reshaped Christianity, leading to new denominations and profoundly impacting European history.