Martin Luther was the prominent reformer associated with the Protestant Reformation in the 16th century. His 95 Theses, nailed to the church door in 1517, critiqued the Catholic Church's practices, particularly the sale of indulgences. Luther's ideas sparked a religious movement that challenged the authority of the pope and questioned the Church's teachings, leading to the formation of various Protestant denominations. The Reformation not only reshaped the religious landscape of Europe but also had lasting social, political, and cultural impacts, contributing to the rise of individualism and changes in governance.