Final answer:
Martin Luther was the first great leader of the Protestant Reformation, a movement that sought to reform the Catholic Church and established Protestant denominations based on faith alone and scriptural authority.
Step-by-step explanation:
Martin Luther was a seminal figure in the Protestant Reformation, a movement that sought to reform the Catholic Church in the 16th century. Luther, a German monk and professor, famously posted his 95 Theses on the door of the Castle Church in Wittenberg, which critiqued various practices of the church, such as the sale of indulgences. His calls for reform led to his excommunication, but the advent of the printing press facilitated the dissemination of his ideas across Europe. Luther emphasized the importance of faith alone for salvation and the supremacy of scripture as the sole authority in Christianity, challenging the Catholic Church's teachings that salvation was achieved through a combination of faith and good works.