Manfred
A lord? A familial dictator? Manfred is both. As The Castle of Otranto's antagonist, Manfred the tyrannical husband of Hippolita and the obsessive father of Matilda and Conrad. The tyranny he inflicts upon his family and those visiting his castle make him a prime example of a Gothic villain. His passion obscures his ability to reason, and he becomes so obsessed with the death of his son that he feels he must divorce his wife and marry his deceased son's intended bride. The terror that ensues following his chase of Isabella is grotesque and morally reprehensible, but it is also the driving force behind the novel's suspenseful plot.
Isabella
Isabella, lovely, virtuous, and self-assured, is this novel's damsel in distress. Threatened by kidnapping, rape, and an overall unwanted marriage, she tries to escape from the castle after the death of her intended husband, Conrad. She narrowly escapes Manfred's grasp, preventing a nearly incestuous and non-consensual marriage from taking place. She is rescued by Theodore, the soon-to-be revealed legitimate heir of Otranto, and marries him during the novel's resolution.
Conrad
The teenage son of Manfred and Hippolita, Conrad is betrothed to Isabella, but on the way to his wedding he is crushed to death by a symbol of the curse of the Otranto castle: a supernaturally-charged falling helmet.
Matilda
Manfred's ultimate display of tyranny occurs when he mistakenly stabs his daughter Matilda to death. Matilda, a young woman of extreme sympathy, virtue, and sentimentalism, falls in love with Theodore; however, unable to get approval from her parents to be with him, she is instead betrothed to Frederic, Isabella's lustful father.
Hippolita
The wife of a villainous lord and the mother to soon-to-be deceased children: these are Hippolita's roles. Manfred desires to divorce his wife because she cannot provide another heir, but he tries to justify the divorce by saying that the couple is actually related. Submissive, excessively religious, and depressed, Hippolita remains under the influence of her husband, catering to his whims despite her own longings for happiness.
Theodore
Theodore, the son of Friar Jerome and savior of Isabella, is the true heir of the Castle of Otranto. His initial role in the novel is to illustrate the relationship between the fallen helmet and the prophecy of the true heir being revealed. He helps Isabella escape from the castle during Manfred's suspenseful pursuit, while also attracting the attention of both Matilda and Isabella. He marries Isabella after the death of Matilda.
Friar Jerome
Isabella escapes to a monastery located outside of the castle where she finds Friar Jerome, the long-lost father of Theodore. Manfred tries to bend the friar to his will by employing the friar to legitimize the divorce, but the plan does not come to fruition. Jerome stands his ground and criticizes Manfred's incestuous and evil desires, saying that heaven does not approve of them.
Bianca
Matilda's tart-tongued and opinionated maidservant who encourages Matilda to marry.
Diego and Jaquez
Two servants in the household who report mysterious sightings of the giant.
The hermit
Frederic discovers this dying hermit in the woods, who imparts a secret that St. Nicholas told hm about the dissolution of Manfred's claim to the Otranto principality.
Alfonso
The handsome and noble ancestor of the castle and principality of Otranto. Theodore resembles him quite strongly.