Final answer:
Martin Luther was the one who independently broke away from the Catholic Church, starting the Protestant Reformation, while John Calvin later developed Calvinism, building upon the changes initiated by Luther.
Step-by-step explanation:
The individual who broke away from the church on their own accord was Martin Luther. Luther was an Augustinian monk and sparked the Protestant Reformation in the 16th century, primarily as a response to the selling of indulgences and other practices he viewed as corrupt within the Catholic Church. His famous Ninety-Five Theses, nailed to the door of the church in Wittenberg, criticized various church practices and ultimately led to his excommunication and the development of Lutheranism. On the other hand, John Calvin, also a key figure in the Reformation, developed Calvinism in Geneva after Lutheranism had already established a precedence for breaking with the Roman Catholic Church. Calvin was influenced by the fragmentation of religious unity that Luther's actions had begun.
A significant difference between Luther and Calvin's approach was their view on salvation and predestination. Calvin's teachings emphasized predestination and a more systematic approach to theology and church organization. While both Luther and Calvin advocated for the Bible's accessibility to ordinary people and questioned the authority of the Pope, it was Luther's actions that directly initiated the Protestant Reformation.