explanation of how i found the answer: John Calvin was a French theologian, pastor and reformer in Geneva during the Protestant Reformation
Thanks it was right!
The correct answer to the question: Which protestant reformer split from the Catholic Church to form a theocracy in Geneva, would be, John Calvin.
John Calvin was a French theologian, lawyer and reformer who always opposed the doctrines of the Catholic Church and ended up generating great reformation, even in the Protestant Movement, especially in Geneva, during the 1500´s. Calvin ended in Geneva after a widespread and pretty violent persecution in France against Protestants, and from 1536 onwards he began to write and publish his famous Institutes of the Christian Religion, which became the framework for the theocracy that was founded later on in Geneva. Two of his most famous beliefs had to do with predestination and also God´s sovereignity in man´s salvation. Calvin played a key role in the reformation, and the new foundation of government and church rules in Switzerland, but most importantly, in Geneva.