Conrad

Fifteen-year-old Conrad makes the briefest of appearances. He has been sickly. He is crushed on his way to marry Isabella by the improbable—and some have argued comic—event of a giant helmet falling from the statue of Alfonso and landing on him. His role is brief but important for setting the plot of the novel in motion. Jerome explains that the death was a fulfillment of prophecy, enraging Manfred.

Manfred

The evil Manfred, lord of the castle of Otranto, became a prototype for the Gothic anti-hero. Becoming obsessed with the idea of establishing an heir, he abuses his patriarchal power to try to achieve his goal. He is not innately evil but becomes a cruel tyrant who will stop at nothing to marry Isabella, his son's former betrothed, who definitely does not want to be his wife. In many ways, Manfred is modeled on King Henry VIII, who divorced his first wife because he feared that their being related blocked him from having a male heir. Manfred is not really related to Hippolita, but that doesn't stop him from clinging to the theory.

Hippolita

Hippolita is Manfred's wife and the mother of Conrad and Matilda. She is a submissive woman who bears her husband's tyrannies. She is also the patroness of the church where Isabella seeks refuge.

Matilda 

Matilda is pure and an object of lust in the story. Frederic, who is old enough to be her father, wants to marry her. She herself fell in love with Theodore before the stabbing. She is morally good and forgives her father for accidentally stabbing her, even though he never loved her.

Isabella

Another pure young woman, Isabella is originally intended to marry Conrad. After his death at the beginning of the story, Manfred claims he will marry her—against her will—to ensure Otranto remains in his possession. She resists marrying the lustful and cruel man and eventually marries Theodore. Together, they become lady and lord of the castle.

Father Jerome

Father Jerome is a friar whose help Manfred seeks in implementing his marriage schemes. He vouches for Isabella and warns Manfred that he will be punished for divorcing his wife for power. He is also Theodore's father.

Theodore

Theodore is the love object of both Isabella and Matilda. He is a good young man who helps the imprisoned Isabella after himself being imprisoned by Manfred. He and Isabella end up marrying, and he becomes lord of Otranto.

The Marquis of Vicenza

The Marquis is Isabella’s father. He comes to Otranto disguised as the Knight of the Gigantic Sabre, intending to claim rightful ownership. He and several hundred men carry a huge sword that is inscribed with a prophecy, reading that only the blood of Manfred can restore the caste to its true heir. After securing Isabella, the Marquis falls in love with Matilda (who is much, much younger than he is). The two do not wed despite his efforts.

Prince Alfonso the Good

The helmet on the statue of Prince Alfonso crushes Conrad at the beginning of the story. He appears to be the giant of the tale, claiming that Theodore is his grandson by birth and is therefore the rightful heir. He then ascends to heaven, apparently having fulfilled his earthly duties.