Martin Luther was a German professor, priest and monk, as well an emblematic figure of the Protestant Reformation. He was known for strongly denying and opposing practices of the Catholic Church, such as indulgences. He also challenged the authority of the Pope and believed the Bible to be the only source of divinely knowledge, directly from God. His work on The Ninety-Five Theses is credited being a catalyst for the movement that would later become known as the Protestant Reformation, during the 16th century.