Don Carlos is the sensitive, twenty-three-year-old heir to the Spanish throne. His relationship with his father, King Philip the Second, is contentious and devoid of love. Don Carlos is tormented by his father's marriage to Elizabeth de Valois, whom he loved prior to her union with the King. This unfulfilled love motivates his desire to leave Madrid and serve as an emissary to Flanders, seeking both to escape his emotional turmoil and to prove his worth. Despite his close friend Roderigo's devotion to his happiness, Carlos' fate seems to be confinement by his father to a monastery. Carlos' character is marked by his enduring but unrequited affection for Elizabeth and his desire to establish his own identity beyond his father's shadow.

Philip the Second, the austere King of Spain, is a man devoid of compassion and love. His rule is characterized by self-interest and an overwhelming sense of jealousy and insecurity. Despite his power, he is easily manipulated by those around him. Philip's only act of forgiveness is towards an admiral who lost a fleet in rough seas, an action more self-serving than altruistic. He frequently blames the church for his personal and political failings, though he is criticized for not seeking its counsel. The king's character is epitomized by his lack of empathy and understanding, making him a ruler feared more than respected.

The Marquis de Posa, known as Roderigo, is a loyal friend and confidant to Don Carlos. His allegiance to Carlos stems from a childhood incident where Carlos defended him. Posa is a hero in every sense, exhibiting both military prowess and intellectual depth. He is known for his beneficence and steadfastness in advocating for improved conditions for humanity. Posa's influence reaches its zenith when he convinces Philip to grant him unrestricted access to the court. Ultimately, Posa's secret life as a member of a religious order and his philosophical ideals of brotherly love cost him his life, leaving a profound impact on Carlos.

Elizabeth de Valois, the Queen of Spain and second wife to Philip, is deeply in love with her stepson, Don Carlos. Her affection for Carlos only intensifies her contempt for the king. Elizabeth's motives are driven by the desire to see Carlos ascend to the throne. Her love for Carlos transforms from a passionate longing to a pure, selfless love, as she supports his fight for the oppressed in honor of Posa. Her death from grief is a testament to the depth of her emotions.

The Duke of Alva is a cunning and loyal agent of King Philip, actively working to undermine Don Carlos. His machinations are supported by other court members who resent the king's favoritism towards Posa. Alva's duplicity is a significant threat to Carlos, further complicating the prince's already dire circumstances.

The Princess de Eboli is an attendant of Queen Elizabeth, embroiled in an affair with King Philip. Her letters to Don Carlos, mistaken for those from the Queen, contribute to the intrigue against Carlos. Eboli's involvement in the conspiracy aligns her with the Duke of Alva, making her a dangerous adversary. Her actions are loathed by Posa, who would have preferred her expulsion from the court.

The Grand Inquisitor, a blind cardinal, plays a pivotal role in the power dynamics of the court. He identifies Posa as a member of a religious order and accuses him of heresy. In a bid to curry favor with the church, Philip delivers Don Carlos to the Inquisitor, hoping to replace Posa with his own son. The Inquisitor's influence is a testament to the pervasive power of the church in Spanish politics.

Domingo,...

Count Lerma, the colonel of the royal bodyguard, is primarily a messenger of both fact and fiction. His role as a talebearer to Don Carlos often leads to confusion and distress for the prince, as Lerma's reports are frequently a mix of truth and speculation.

The Marchioness de Mondecar, a devoted attendant to the Queen, sacrifices her position to protect Elizabeth. She is dismissed from service after admitting she was the one in the garden with Carlos, an action that reflects her loyalty to the Queen's happiness over her own standing.

Don Raimond de Taxis, the postmaster general, plays a crucial role in revealing the truth about Posa's intentions. By disclosing Posa's letters, which insinuate Posa's romantic involvement with the Queen, Taxis inadvertently vindicates Don Carlos. However, this revelation ultimately leads to Posa's murder, highlighting the perilous nature of court intrigues.

Don Luis Mercado, the Queen's physician, facilitates the final meeting between Don Carlos and Elizabeth. His involvement is crucial, as he provides Carlos with a disguise to secretly enter the Queen's chambers, demonstrating his willingness to aid in their clandestine affairs.

The Duke of Medina Sidonia, the Admiral of the King's fleet, is forgiven by Philip for his negligence in losing a fleet. This act of clemency is less about the Duke's redemption and more about enhancing the King's image as magnanimous, reflecting Philip's calculated approach to leadership.

The Marquis de Posa, or Roderigo, is a friend of Don Carlos's. He swore loyalty to Carlos and is a superb soldier, confidant, thoughtful, and secretly a member of a religious order.