Martin Luther was a German theologian and monk who initiated the Protestant Reformation in the 16th century. Born in 1483, he challenged the Catholic Church’s practices, especially the sale of indulgences. In 1517, he famously nailed his 95 Theses to a church door in Wittenberg, sparking widespread debate. Luther emphasized salvation by faith alone and the authority of Scripture over Church tradition. He translated the Bible into German, making it accessible to ordinary people. His actions led to the formation of Protestant churches and reshaped Christianity in Europe. Luther died in 1546, but his influence remains significant in religious history.