Bishop Cuthbert Tunstall is a minor character in Seasons One, Two and Three of The Tudors. His exact Bishopric is never established, but he is shown to be a close associate of Archbishop William Warham until the latter's death. In episode 1.08, Tunstull and Warham attempt to browbeat Queen Catherine of Aragon into conceding to King Henry's annulment (by accusing her of intemperate and malicious behavior) but she realizes they have been bribed/threatened by Henry into doing so and sees through their feeble arguments, calling them out on their immorality. Nonetheless, Tunstall takes Henry's side during the subsequent debate at Westminster about the annulment. He angrily shouts down Catherine's strongest supporter, Bishop Fisher, when the latter compares Henry to the biblical King Herodd for seeking divorce for sexual reasons.
After Warham's death (episode 2.02), Tunstall sides with the Reformation faction, though he remains tentative friends with the devoutly Catholic Sir Thomas More. However, when Tunstall (again acting as a mouthpiece for the King) visits More in 1.03 and asks him why he refused an invitation to attend Queen Anne Boleyn's coronation, More coldly affirms that his loyalty to the King will always come second to God and the Catholic Church, earning him Tunstall's disapproval. Nonetheless, Tunstall attempts to save More during his questioning in 2.04, pleading for More to take the Oath recognizing Henry's Acts of Succession and Supremacy. However, More still refuses to recognize Henry's Protestant Church, leading to his arrest and execution in the next episode.
Tunstall is seen briefly in episode 3.05 alongside Bishop Stephen Gardiner, suggesting that he has broken away from the Protestant faction at Court and rejoined the more conservative clergy. He is shown reading the Six Articles of Faith with Gardiner (which returns England's Church to a doctrine almost identical to Catholicism) before Henry, who then signs them into law, to Tunstall and Gardiner's satisfaction.