John Calvin, the theologian and pastor, was influential in the field of religious theology and the Protestant Reformation. He is best known for his role in the development of Calvinism, a branch of Protestant Christianity, which he outlined in his seminal work, "Institutes of the Christian Religion." Calvin's teachings and ideas had a profound impact not only on religious doctrine but also on the social, political, and economic aspects of society in the regions where Calvinism took root. His emphasis on predestination, the sovereignty of God, and the importance of individual piety and good works continue to shape theological discussions and have a lasting influence on Protestant Christianity to this day.