Martin Luther OSA ( 10 November 1483 – 18 February 1546) was a German monk, former Catholic priest, professor of theology and seminal figure of a reform movement in 16th century Christianity, subsequently known as the Protestant Reformation. He strongly disputed the claim that freedom from God's punishment for sin could be purchased with monetary values. He confronted indulgence salesman Johann Tetzel, a Dominican friar, with his Ninety-Five Theses in 1517. 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 Diet of Worms in 1521 resulted in his excommunication by the Pope and condemnation as an outlaw by the Emperor.
Luther taught that salvation and subsequently eternity in heaven is not earned by good deeds but is received only as a free gift of God's grace through faith in Jesus Christ as redeemer from sin and subsequently eternity in Hell. 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 from God and opposed sacerdotalism by considering all baptized Christians to be a holy priesthood. Those who identify with these, and all of Luther's wider teachings, are called Lutherans even though Luther insisted on Christian as the only acceptable name for individuals who professed Christ.