Manfred, the lord of the castle of Otranto, embodies the archetypal Gothic anti-hero. Driven by an obsession to establish a male heir, he becomes a tyrannical figure, willing to forsake moral and familial bonds to achieve his ambitions. Despite not being innately evil, Manfred's lust for power transforms him into a cruel tyrant, willing to divorce his wife Hippolita and forcibly marry Isabella, his deceased son's betrothed, to maintain control over Otranto. His actions mirror those of King Henry VIII, as he irrationally believes that his marriage to Hippolita, whom he is not related to, impedes his quest for an heir. After a series of ominous supernatural occurrences, Manfred ultimately abdicates his claims to Otranto, entering a convent alongside his wife in penance.

Theodore, first introduced as a mere peasant, is revealed to be the true heir to the throne of Otranto. He becomes the romantic focus of both Isabella and Matilda. Captured and nearly executed under Manfred's orders, Theodore's fate turns with the aid of both human allies and supernatural forces. His lineage is disclosed when Father Jerome, a former prince turned priest, recognizes him as his own son. Through these revelations and his eventual marriage to Isabella, Theodore claims his rightful place as the new lord of Otranto.

Father Jerome, once the prince of Falconara, now serves as a priest. He becomes an unwitting participant in Manfred's schemes, initially sought for his clerical assistance in legitimizing Manfred's attempts to marry Isabella. Jerome emerges as a pivotal character when he discovers that Theodore, whom he is called to absolve, is his own son. He acts as a moral compass, warning Manfred against his divorce and remarriage, and ultimately supports Theodore's rightful claim to Otranto.

The Marquis of Vicenza, Isabella's father, arrives in Otranto disguised as the Knight of the Gigantic Sabre, determined to assert his daughter's rights. Bearing a massive sword inscribed with a prophecy, he seeks to restore the castle's legitimate heir. His misguided affection for Matilda complicates his role, as he briefly entertains a betrothal to her to gain Manfred's consent for his own marriage to Isabella. However, he ultimately renounces Matilda, swayed by ominous warnings and supernatural interventions.

Isabella, the daughter of the Marquis of Vicenza, is initially engaged to Conrad. Following Conrad's untimely demise, she becomes the object of Manfred's unwanted attention, as he seeks to marry her to secure his hold over Otranto. Isabella, embodying purity and resistance, evades Manfred’s advances with the assistance of Theodore, the rightful heir to Otranto. Ultimately, she marries Theodore, and together they become the new rulers of the castle.

Hippolita, the submissive wife of Manfred, endures her husband's tyrannies with quiet resilience. She is the mother of Conrad and Matilda and serves as the patroness of the church where Isabella seeks refuge. Throughout the narrative, Hippolita's character highlights the theme of female subservience in a patriarchal society. Following the supernatural events, she retreats to a convent, seeking solace and redemption away from the turmoil of the castle.

Matilda, Manfred's daughter, is characterized by her moral purity and tragic fate. Despite being the object of Frederic's desire, she harbors love for Theodore. In a tragic twist, she becomes a victim of her father's jealousy. Mistaking her for Isabella, Manfred accidentally stabs Matilda, bringing about profound remorse. Even in her dying moments, she extends forgiveness to her father, solidifying her character as one of moral integrity.

Conrad, the fifteen-year-old son of Manfred, plays a crucial albeit brief role in the narrative. Sickly yet destined for a marriage to Isabella, his life is abruptly ended when a giant helmet—a bizarre...

Prince Alfonso the Good, the former ruler of Otranto, influences the narrative from beyond the grave. The helmet from his statue is the instrument of Conrad's death, setting the novel's events into motion. His spectral appearance serves to reveal Theodore as his grandson and rightful heir. Having fulfilled his purpose, Alfonso's spirit ascends to heaven, with Saint Nicholas receiving him.

Saint Nicholas, who receives Prince Alfonso into Heaven.