- Martin Luther, a German theologian and religious reformer, initiated the Protestant Reformation in the 16th century. Luther criticized various practices and teachings of the Catholic church, particularly the concept of indulgences and the authority of the Pope. He believed that salvation could be attained by faith alone, not through good works or indulgences.
- John Calvin, a French theologian and reformer, developed a system of Christian theology known as Calvinism. He emphasized the idea of predestination, stating that God predetermines who will be saved or damned, independently of any human merit or action. Calvin also emphasized the importance of Scripture, church discipline, and a strict moral code.