Martin Luther was a German monk and theologian who played a key role in the Reformation, a movement in the 16th century that sought to reform the practices and beliefs of the Roman Catholic Church. In 1517, he famously nailed his Ninety-Five Theses to the church door in Wittenberg, criticizing the sale of indulgences and other church practices he viewed as corrupt. Luther's actions sparked widespread debate and led to the establishment of Protestantism, a branch of Christianity that broke away from the Catholic Church. His translation of the Bible into German made the scriptures more accessible to the general public, promoting individual interpretation of the faith.