Caligula (Caius) is the young Emperor of Rome whose initial reputation as a good ruler shifts abruptly following a personal loss. Motivated by the realization that humans die without finding happiness, he adopts a perspective of strict, unyielding logic. He uses his absolute state power to force the patricians to confront the meaninglessness of their societal rules. Rejecting all social limits, he expresses a desire to achieve the impossible by attempting to literally capture the moon.

Cherea is a well-reasoned literary man and philosopher among the Roman noble class. His peers simply fear the emperor's cruelty, but Cherea clearly understands the underlying logic of the new imperial worldview. He values a safe, predictable society over absolute logical consistency and actively organizes opposition to protect the world from nihilistic destruction.

Scipio is a young Roman citizen with a sensitive, artistic disposition. He holds a deep, genuine affection for the emperor at the beginning of the play, actively choosing to look for the good in him. The state's increasingly brutal decrees test his loyalty, leaving him torn between his inherent tenderness and his horror at the government's actions.

Caesonia is the emperor's faithful mistress. She maintains a steady confidence in her position within the imperial court and stands apart from the panicking patricians. In private moments, she attempts to offer the emperor comfort and address his emotional state, holding onto the belief that affection and human connection hold lasting value.

Helicon is a young assistant and close associate of the emperor. He approaches the extreme decrees and the resulting societal devastation with an attitude of unconcern. He literalizes the emperor's metaphors and acts as an unquestioning instrument of the imperial will.

Drusilla is the emperor's recently deceased sister. Her sudden death initiates the central conflict by sparking the emperor's philosophical awakening and his subsequent behavioral shift. She represents the fragility of human life and the abrupt end of meaningful connection.

Lepidus is a Roman nobleman who suffers directly under the new system of logic. He typifies the older patrician class. He attempts to survive the regime through polite compliance, even when subjected to intense psychological cruelty regarding his own executed family.

Mucius is a member of the Roman patrician class. He demonstrates the court's helplessness when the emperor exerts extreme control over the personal lives and bodily autonomy of the nobility.

Mereia is a Roman patrician caught in the emperor's web of suspicion. His interactions with the ruler demonstrate the unpredictable and lethal nature of the new imperial logic, where mere suspicion carries fatal consequences.