Final answer:
Christians who protested against the practices and beliefs of the Roman Catholic Church during the sixteenth century became known as Protestants, leading to the Protestant Reformation initiated by key figures such as Martin Luther and John Calvin.
Step-by-step explanation:
Christians who protested against Roman Catholic beliefs came to be known as Protestants. This movement began in the early sixteenth century with figures like Martin Luther and John Calvin, and it led to what is now referred to as the Protestant Reformation. Martin Luther's protest against the Church's sale of indulgences and his teachings that faith alone was needed for salvation were a critical starting point for this momentous change. These religious reformers sought to purify Christian practices and beliefs and believed that scripture alone should be the authority on matters of faith and doctrine.
The Church of England also saw internal protests, with King Henry VIII forming the Anglican Church out of protest against the Catholic Church. Additionally, groups like the Puritans and Separatists sought to eliminate Catholic practices from the Church of England, pressing for a return to what they saw as a purer form of worship and doctrine.