Martin Luther is an unseen character in The Tudors. A German monk and professor of theology from Dresden, Saxony, Luther was arguably the most pivotal figure of the Protestant Reformation. He disagreed with many practices and teachings of the Catholic Church during the Late Medieval Period and the Renaissance, especially the selling of indulgences for the forgiveness of sins.
In 1517, early in Henry VIII's reign, he denounced the corruption of the Papacy through his book, The Ninety-Five Theses. Among many other things, Luther argued that salvation came through faith rather than through good deeds or the sale of indulgences, and that the Bible was the only source of divine knowledge, rather than the priesthood and the Clergy. By doing so, he directly challenged the authority of Pope Leo X and angered the devoutly Catholic Holy Roman Emperor, Charles V; after attending the Diet of Worms in 1521, Luther refused to retract his writings as demanded by the Pope and Emperor. As a result, he was declared an outlaw and heretic and excommunicated, but Prince-Elector Frederick III of Saxony, who was impressed by Luther's arguments, gave him safe haven and allowed him to continue his writings. Luther's work inspired many followers and scholars to challenge Papal authority in many parts of Europe, beginning the Protestant Reformation in Germany, Scandinavia and the Low Countries. Luther set the precedent for the removal of the vows of celibacy on Lutheran priests (through his own marriage to Katharina von Bora) and the translation of the Bible from Latin to German, which made it much more accessible for the under-educated throughout the Empire. He died in 1546, only a year before Henry VIII.
In Season One of The Tudors, though Luther never actually appears, he is frequently mentioned. Sir Thomas More, in "Simply Henry" remarks to Cardinal Wolsey that "so long as there is such blatant corruption in the Church, that heretic Luther will continue to gain followers!" indicating that, despite his own devout Catholicism, More understands what drives Luther to defy the Pope. In Episode 1.03, "Wolsey, Wolsey, Wolsey!" More tells Imperial Ambassadors that he hears that Lutheranism is spreading across Germany "like a forest fire"; he later states to his daughter Margaret that, despite his own dislike for violence, he believes "Luther and every one his followers should be seized, right now, and burned." (1.07)
King Henry (who, at this point, remains devoutly Catholic) is writing a strongly-worded pamphlet that denounces Luther and affirms the supremacy of the Pope. He asks More to take a copy to Rome, and to destroy every piece of Lutheran literature he can find in England. More returns in "His Majesty the King" having received the Pope's congratulations to Henry and grateful bestowing of the title "Fide Defenso" (Defender of the Faith) but he adds that Luther himself has also responded to Henry's work, accusing the King of "prattling like a strumpet in a tavern." This naturally enrages Henry, who says that Luther ought to be burned at the stake.
Meanwhile, Henry's new secretary, Thomas Cromwell, attends a secret meeting of German Lutherans in London; he grins approvingly at their descriptions of the Reformation as a source of spiritual liberty. By episode 1.08, Henry's arguments with the Pope over the annulment of his marriage to Catherine of Aragon have made him much more receptive to the arguments of the Protestants, especially on Royal Supremacy (which was put forward to him by Cromwell and Anne Boleyn). When discussing Luther with Ambassador Chapuys, Henry states "You see, when Luther denounced the corruption of the Clergy, he was right. Had he stopped there, and not gone on to destroy the Sacraments, I would gladly have raised my pen in his defense, rather than attacking him." This indicates that, although he is unwilling to reverse his previous denouncement of Luther, Henry has at least developed a great respect for him.
Ironically, despite his opposition to the Papacy, Luther condemned Henry for his poor treatment of his Catholic first wife, Catherine of Aragon- out of respect for her piety, and recognizing that Henry was breaking with Rome for selfish reasons rather than a desire for genuine reform.