Manfred is the Prince of Otranto, a greedy and autocratic ruler desperate to maintain his family's grip on the castle. Following a sudden and bizarre tragedy on his son's wedding day, he becomes increasingly erratic and tyrannical. Fearful of an ancient prophecy that predicts the end of his lineage's rule, he decides to disregard morality and Christian virtue to secure a new male heir by any means necessary.

Hippolita is the pious and compassionate wife of Manfred. She completely submits to the patriarchal structure of Otranto, absorbing her husband's cruelty and defending his behavior to others. Even as Manfred plots against her own standing to secure his political future, she relies entirely on her faith and remains obedient to his commands.

Matilda is the teenage daughter of Manfred and Hippolita. Ignored by her father because she is not a boy, she finds solace in her mother's affection and her strong religious faith. She initially hopes to enter a convent, but the chaos in the castle and the arrival of a brave young peasant challenge her plans for the future.

Isabella is the beautiful daughter of the Marquis of Vincenza. Originally brought to Otranto as a political pawn to marry Conrad, she quickly transforms into a fugitive running for her life through dark, subterranean tunnels. She seeks sanctuary in the Church of St. Nicholas to escape Manfred's aggressive schemes, relying on the help of strangers to survive.

Father Jerome is a friar at a nearby convent who embodies divine authority and Christian morality. He stands as a direct obstacle to Manfred's political greed, refusing bribes and threatening excommunication to protect the innocent. He uses the sanctuary of the church to shield vulnerable individuals from the prince's tyranny.

Theodore is a young peasant laborer who happens to bear a striking physical resemblance to the revered former ruler, Alfonso the Good. His perceptive nature quickly makes him a target for Manfred, who baselessly accuses him of treason and sentences him to death. Despite his low social standing, he displays incredible bravery and a strong sense of justice.

Frederic is the Marquis of Vincenza and Isabella's father. A blood relative of Alfonso the Good, he has been missing for years after being captured during the Crusades. He returns to Otranto following a strange vision, intent on reclaiming his daughter and asserting his own political rights over the castle.

Conrad is the sickly, weak son of Manfred and Hippolita. As the only male heir to the Otranto dynasty, his arranged marriage to Isabella is entirely political. His sudden and bizarre demise on his wedding day serves as the catalyst for the entire supernatural crisis in the castle.

Alfonso the Good is a former, highly respected ruler of Otranto. Though deceased, he maintains a powerful presence over the castle, both as an object of religious worship for Hippolita and Matilda, and as a supernatural force seemingly determined to purge the castle of its current illegitimate rulers.

Bianca is a loyal, talkative servant attending to Matilda and Hippolita. She is highly superstitious and easily frightened by the supernatural events plaguing the castle. She often provides rumors and practical observations to the isolated royal women she serves.

Diego is a servant in Manfred's household. He is one of the staff members who experiences the castle's horrifying supernatural manifestations firsthand, contributing to the atmosphere of panic that gradually engulfs the estate.

Jaquez is another servant working in the Castle of Otranto. Like the rest of the staff, he is completely overwhelmed by the magical and terrifying events disrupting the household, serving as a messenger of bad news to his increasingly volatile master.