Final answer:
Martin Luther, a German monk and professor of theology, initiated the Protestant Reformation in 1517 by posting his 95 Theses, which challenged the Catholic Church's practices and doctrines, specifically the selling of indulgences.
Step-by-step explanation:
The person who helped spark the Protestant Reformation in 1517 was Martin Luther, a German monk and professor of theology. Luther's posting of his 95 Theses on the door of the Castle Church in Wittenberg challenged the Catholic Church's practice of selling indulgences and called for a return to the scriptures as the sole authority in Christian life. His actions led to his excommunication and the spread of Protestantism throughout Europe, facilitated by the printing press.
Luther's ideas on faith and salvation diverged significantly from Catholic doctrine. He argued that faith alone was needed for salvation, a direct challenge to the Church's teachings on indulgences. The printing press enabled his writings to reach a wider audience, and as a result, his ideas became a catalyst for religious reform and the eventual division of Christianity in Europe.
Although Luther simply wanted to reform the Catholic Church, the outcome was a new movement. The resulting religious, social, and political changes had a profound impact on European history, leading to the establishment of various Protestant sects, and influencing the direction of Christianity as a whole.