In 1517, Martin Luther initiated the Protestant Reformation by publishing his Ninety-Five Theses. Luther, a German monk, criticized the Catholic Church's practices, particularly the sale of indulgences, which he saw as a corruption of true Christian doctrine. His theses sparked widespread debate and were rapidly disseminated across Europe thanks to the printing press. This movement challenged the authority of the Pope and led to the formation of various Protestant denominations. Luther's actions marked a significant religious transformation, creating lasting changes in Christianity and society and ultimately contributing to the development of modern Western thought and culture.