French theologian and pastor (1509-1564), the most systematic mind of the Protestant Reformation. Trained in law and classical humanism, he converted in his early twenties and fled France for Switzerland. His Institutes of the Christian Religion — first published 1536 as a small manual, expanded over 23 years into a four-volume systematic theology — remains a pillar of Reformed thought. For most of his ministry he labored in Geneva as chief pastor, lecturer, and civic adviser, turning the city into the training ground for a generation of Reformed pastors sent across Europe.
Calvin's contribution is comprehensive biblical exposition combined with rigorous dogmatics. He wrote commentaries on almost every book of the Bible — careful, grammatical, Christ-centered. His Institutes organize theology around the knowledge of God and the knowledge of ourselves. He is best known for the so-called "five points" (TULIP — not coined by Calvin but a useful summary of Synod of Dort-era Reformed distinctives): Total depravity, Unconditional election, Limited atonement, Irresistible grace, Perseverance of the saints. But limiting "Calvinism" to those five points misses most of him. Calvin contributed enormously to: ecclesiology (plural eldership, four offices — pastor, teacher, elder, deacon), worship (regulative principle, psalm-singing), education (the Academy of Geneva), and political theology (lesser magistrates, resistance theory). His pastoral letters show a warm, engaged shepherd — quite different from the cartoon "cold Calvin" caricature. His one infamous failure — consent to the execution of Servetus in 1553 — reflects his era more than his distinctive theology; still, it remains a cautionary example of church-state entanglement.