John Calvin was a French theologian, pastor, and reformer during the Protestant Reformation in the 16th century. He is best known for his influential work in shaping the doctrines of the Reformed tradition and for his role in establishing the Presbyterian system of church government. Calvin's most famous work is "Institutes of the Christian Religion," which outlined his theological beliefs and had a significant impact on the development of Protestant theology. His teachings emphasized the sovereignty of God, predestination, and the authority of scripture. Calvin's ideas had a lasting impact on the development of Protestantism and continue to influence Christian theology and church practice to this day.