Martin Luther (10 November 1483 – 18 February 1546) initiated the Protestant Reformation. As a priest and theology professor, he confronted indulgence salesmen with his The Ninety-Five Theses in 1517. Luther strongly disputed their claim that freedom from God's punishment of sin could be purchased with money. His refusal to retract all of his writings at the demand of Pope Leo X in 1520 and the Holy Roman Emperor Charles V at the Edict of Worms meeting in 1521 resulted in his excommunication by the pope and condemnation as an outlaw by the emperor. Martin Luther taught that salvation is not from good works, but a free gift of God, received only by grace through faith in Jesus as redeemer from sin. His theology challenged the authority of the pope of the Roman Catholic Church by teaching that the Bible is the only source of divinely revealed knowledge and opposed sacerdotalism by considering all baptised Christians to be a holy priesthood. Those who identify with Luther's teachings are called Lutherans.

His translation of the Bible into the language of the people (instead of Latin) made it more accessible, causing a tremendous impact on the church and on German culture. It fostered the development of a standard version of the German language, added several principles to the art of translation, and influenced the translation into English of the King James Bible. His hymns inspired the development of singing in churches. His marriage to Katharina von Bora set a model for the practice of clerical marriage, allowing Protestant priests to marry.

Much scholarly debate has focused on Luther's writings about the Jews. His statements that the Jews' homes should be destroyed, their synagogues burned, money confiscated, and liberty curtailed were revived and used in propaganda by the Nazis from 1933 to 1945. As a result of this and his revolutionary theological views, his legacy remains controversial.