Martin Luther was the central figure in the Protestant Reformation. In 1517, he famously challenged the Catholic Church's practices by posting his Ninety-Five Theses, which criticized the sale of indulgences and called for reform. Luther's writings and teachings emphasized salvation through faith rather than through the Church's intermediaries. His beliefs led to significant theological and social shifts, sparking broader movements across Europe that questioned church authority. The Reformation ultimately resulted in the formation of various Protestant denominations and profound changes in Christianity's role in society, politics, and governance.