Final answer:
John Calvin, a French lawyer who converted to Lutheranism, fled persecution in France and settled in Geneva, making it a pivotal center of the Protestant Reformation.
Step-by-step explanation:
The Frenchman who converted to Lutheranism and was forced to flee persecution by the French king was John Calvin (Jean Calvin). After his conversion, he found refuge in Geneva, which he transformed into a major center of Protestant thought and influence. His proposed reforms and theological teachings such as predestination markedly differentiated from Lutheranism and had a significant impact on the spread of Calvinism throughout Europe, with followers establishing churches in countries like the Netherlands, Scotland, and France.