The protagonist of Calderón de la Barca’s play is Segismundo, the prince of Poland, who has been imprisoned in a remote tower fortress since childhood. The principal antagonist may be considered King Basilio, his father, who told everyone that his son had died and then placed him in the tower to prevent him from destroying the kingdom. However, Basilio’s intentions were not basically evil, as his decision was influenced by astrologers who predicted that the boy would grow up to become a monster.

Basilio's nephew Astolfo, the duke of Muscovy, has a strong claim to the throne because Segismundo is thought to be dead. Astolfo is the other main antagonist. Ambitious to become king, he is Segismundo’s principal rival.

Living in almost total isolation, Segismundo grows to young manhood unfamiliar with social conventions. When his father becomes concerned about the issue of succession, he has the youth removed from hiding and taken to court in Warsaw. Segismundo’s bad behavior so alarms his father that he has son returned to the tower, where he is told that the whole court episode was a dream.

Another sympathetic, significant character is Rosaura. Her role is pivotal because she helps Segismundo understand the relationship between dreams and reality, and the benefits of morally correct behavior.

One important character who cannot be rigidly classified is Clotaldo. This elderly man serves both as Segismundo’s jailer, which is an antagonistic position, and as his tutor and one of his few companions in the tower.