Final answer:
Martin Luther, a German monk and theology professor, sparked the Protestant Reformation by nailing his 95 Theses to a church door in Wittenberg in 1517, protesting Catholic Church practices, especially the sale of indulgences.
Step-by-step explanation:
Martin Luther, a German monk and Professor of Theology at the University of Wittenberg, is renowned for initiating the Protestant Reformation. In 1517, Luther nailed his 95 Theses to the door of the Castle Church in Wittenberg, Germany, to protest against the selling of indulgences and other practices of the Catholic Church that he found corrupt. This act did not intend to create a new denomination but hoped for reform within the Church. Nevertheless, the consequence was a considerable transformation in European Christianity, leading to the formation of Protestant denominations.
Luther's criticism of practices such as the sale of indulgences, and his theological views that salvation is attained through faith alone and that scripture is the sole authority in religious matters, found resonance across Germany and Scandinavia aided by the invention of the printing press. Despite the Church's subsequent condemnation of Luther as a heretic and his excommunication, Lutheranism—a doctrine based on his reforms—spread widely and became the basis of the Lutheran denomination.