Bishop Eustace Chapuys is the ambassador of Spain (and, by extension, the Holy Roman Empire) to England throughout most of the series. He is also the only character apart from Henry VIII and Charles Brandon to appear in all four seasons portrayed by the same actor (Mary Tudor was portrayed as a young girl in season 1). A shrewd Italian Savoyard by birth, Chapuys is very devoted to his Catholic faith and has a strong friendship with Catherine of Aragon and, later, her daughter Mary. He becomes increasingly appalled by the Reformation and by Henry's brutal reprisals against any sect that attempts to deny his authority; nonetheless, he continues to serve as Ambassador to England until episode 4.08, and remains a devoted friend and advisor to Mary. He is played by Irish actor Anthony Brophy in a recurring role.
Season One 
Eustace Chapuys, a minor bishop of the Holy Roman Empire, first appears in episode 3 of The Tudors as secondary diplomat, accompanying the current Spanish Ambassador, Senor Mendoza, on behalf of Emperor Charles V. Chapuys is initially pleased to hear of King Henry's commitment to Catholic fundamentalism, but he soon realizes that Henry is in fact breaking away from the influence of Rome. Near the end of the season, Mendoza retires and Chapuys takes over his duties. He attempts to plead with Thomas Boleyn to help quell the religious strife of England but is shocked and offended by Boleyn's brazen denounciation of the Catholic Church (the Boleyns were Protestant reformers and gain influence through this in Season 2) and on later occasions, he refers to Boleyn privately as a true agent of Satan.
Although he is initially so offended that he refuses to attend Henry's court, Chapuys finds a more comfortable niche by communicating with Sir Thomas More and the increasingly unfavored Catherine of Aragon, both of whom are devout Catholics. Unlike More, however, Chapuys realizes Henry's threats to break with Rome are not idle, grimly noting that the two people now closest to the King(Thomas Cromwell and Anne Boleyn) are both Reformers.
Chapuys is increasingly alarmed as the Reformation gains pace, but can do little to interfere directly because England is in alliance with France, checking the power of the Papacy-backed Holy Roman Empire. He has a particularly strong hatred for Anne Boleyn (shared by Lady Mary Tudor, with whom he becomes good friends) and refers to her as a whore and a concubine in private. When the Pope suggests someone should 'get rid' of Anne, Chapuys recruits a Catholic Englishman, Henry's groom, to assasinate her, but he fails twice and draws Henry's attention. The assasin, William Brereton, tells Chapuys he can try again, but Chapuys sharply tells him not to act without orders, since Emperor Charles is busy with a war against the Turks and is now seeking to make a new agreement with King Henry; if Brereton were captured in the attempt, he would be tortured for information and Anglo-Spanish relations would be irreparably destroyed.
When Henry talks with Chapuys he mentions how he knows Chapuys does not approve of his religious policies, but insists that he intends to make an everlasting and beneficial reformation to the Church of England. Chapuys, clearly doubtful, darkly remarks "I have no doubt that Your Majesty will always be remembered." He is stunned and angered by the deaths of Sir Thomas More and Bishop Fisher, though he can do nothing.
Chapuys offers comfort to the exiled Catherine of Aragon and her daugter Mary until Catherine dies in episode 2.07, even attempting to communicate with Henry on their behalf (to no avail). Chapuys also fears that Anne Boleyn intends to kill Mary becuase they hate each other, and indeed Anne is shown to remark that "I wish she (Mary) would join her mother" though she never actually attempts to harm Mary. When Brereton reports that Anne's handmaidens have supposedly seen evidence of her being a witch, Chapuys grudgingly authorizes another assasination attempt, at Brereton's insistance that they must 'break the spell' she holds over Henry.
When Anne Boleyn repeatedly fails to provide Henry with a son, Chapuys views it as a sign of God's will that Mary remains a candidate for the Throne, to restore Catholicism to England. Knowing Anne and her family have plummeted from the King's favor after her second miscarriage, he acts politely disdainful when George and Thomas Boleyn (who previously treated him with supreme contempt) make pathetic attempts to ingratiate themselves to him in Episode 2.09. Chapuys instead favors negotiating with the King's secretary and Chancellor Thomas Cromwell, whom he seems to like despite their religious differences; the Protestant Cromwell wants an alliance with Spain now that relations with France are deteriorating, and he clearly intends to destroy Anne Boleyn if necessary for this to happen. Chapuys offers the king a deal from the Emperor; he will recognize Anne Boleyn as Queen now that Catherine is dead, and join him in alliance, but only if Mary is declared legitimate heir to the throne once again. Despite Anne's lack of influence (her imminent fall from power is clear to the entire court), Henry angrily rejects the proposal, as he will not reverse the annulment of his former marriage to Catherine, much to Chapuy's dissapointment. In the Season finale, both Chapuys and Mary show satisfaction at the imminent death of Queen Anne.
Season Three 
In Season Three, with Anne Boleyn dead and Henry's new marriage to Jane Seymour approved by Catholic Europe, Chapuys is hopeful that Spain can form stronger ties with England; however, the Protestant Reformation continues under Cromwell's direction, drawing ire from both Spain and France. Chapuys secretly hopes a combined attack by Spain and France can overthrow Henry and place his Catholic eldest daughter, Mary Tudor, on the throne (he previously asked Queen Jane to persuade Henry to make Mary his heir apparent again; Jane liked the idea, but died before she could do so). Although Mary's greatest adversary, Anne Boleyn, is no more, Henry refuses to have anything to do with Mary unless she recognizes him as Head of the Church of England and that her mother's marriage to Henry was annulled, removing her from the line of succession. Despite this, Chapuys continues to plead on Mary's behalf to Henry, carries messages for her and gives her friendly advice; Mary is extremely grateful to him.
When Cromwell issues a new repressive decree early in the season, Chapuys explains to Mary that the Emperor cannot protect her as he is seeking an alliance with England and does not want to provoke Henry. Chapuys also says that the Emperor is not bound by any law to protect her as she is not a subject of the Spanish Crown. Furthermore, if she does not sign the oath acknowledging Henry, her father will offer her no protection if Cromwell tries her for heresy and condemns her to death; Chapuys begs her to sign the document to save herself, while privately retaining her own faith. Mary reluctantly signs the Oath, asking Chapuys to help her acquire papal absolution for doing so. King Henry, influenced by Cromwell, later accuses Chapuys' master of conspiring to go to war with England alongside France; Chapuys sharply denies these rumors, which have some basis but are in fact untrue, since Emperor Charles is more interested in fighting the Ottoman Turks (who are allied with France).
Season Four 
Chapuys appears more sparsely in Season Four; he has aged consideraby and is increasingly crippled by gout as the season progresses. Although he is increasingly disgusted with Henry's brutal and impulsive policies, he still continues to advocate for an alliance between Spain and England, and is delighted in episode 4.06 when Henry finally agrees to join Charles in a war against France in return for England's lost French territories. However, by episode 4.09 this alliance finally breaks down as all three kingdoms are bankrupt and exhausted by siege warfare, and desperate for peace.
He remains devoted to Mary, comforting her when she is treated harshly by Katherine Howard, and pointing out that many English Catholics believe she has a stronger claim to the throne. Chapuys, although not instructing Mary, makes it clear that both he and the Emperor would still like to see Mary return to the throne and restore Catholicism to England; however, he seems somewhat uneasy about her declaration that she will "burn as many heretics as it takes" to get there. Although fundamentally Catholic, Chapuys seems to be more tolerant than Mary and various others, having nothing but praise for Queen Catherine Parr despite knowing she is a Protestant (this was also shown briefly in Season Two when Chapuys demonstrated his wholehearted willingness to work with the equally Protestant Thomas Cromwell).
When Chapuys retires and departs England for good in episode 4.08- by now crippled to the point that he has to walk with double canes- he and Mary part as friends once again. Henry happens to be in ill humor towards Emperor Charles, but he nonetheless seems put out by the fact that Chapuys is leaving, and wishes him a happy retirement Before leaving, Chapuys gives Mary an ornate ring, a gift to him from her cousin the Emperor- who, in turn, recieved it from her mother, Catherine of Aragon. In episode 4.09, Mary is saddened to hear from Sir Richard Riche that Chapuys has died of old age.
- "Madame, I pray you, don't give way." (to Catherine of Aragon)
- "The King, in his blindness, fears no-one but God."
- "If you succeed in killing the King's whore, you shall be the beloved of God, of His Holiness the Pope, and truly, of all the faithful in England." (to William Brereton)
- William Brerton:(watching Anne Boleyn) "I could still do it. I could find a way to poison her." Chapuys: "No." William Brerton: "But,I thought that was-" Chapuys: "It would be blamed on my master; at the moment, he doesn't need that, he has a war with the Turks to contend with." Brereton: "But why should they ever know." Chapuys: (getting annoyed) "Don't be stupid, Brereton- they would torture you, and you would tell them everything." Brereton: "No, I wouldn't. I'd die a martyr's death." Chapuys:(snorts sarcastically) "You've never even seen a man being tortured, have you? You understand? You don't act alone."
- (on Thomas Boleyn) "I truly believe that man to be an emmisary of Satan."
- "The brat is now officially a bastard." (referring to Elizabeth Tudor)
- (on Anne Boleyn) "I am told that she blames me for her current predicament... of course, I take this as a compliment."
- "What lady on Earth would be willing to marry a king who either puts his wives away... or kills them?"
- "My poor, sweet lady." (consoling a crying Mary Tudor)
- Mary Tudor: "Tell me what is happening at court. Is the King thinking of marrying again?" Chapuys: "There is a new law enacted. It requires that any lady the king may marry must, on pain of death, disclose any charge of sexual misconduct that might be brought against her. Frankly, my lady, this lowers the field. The ladies at court are how you say... not exactly known for their virtue."
- "Your Grace could not have made me happier if you had brought me a cure for gout." (to Charles Brandon, on hearing Henry will accept an alliance with Spain.)
- Mary Tudor: "You are, and always have been... my most faithful and truest friend in all the world."