Manfred, the prince of Otranto, a usurper. After Manfred’s son is mysteriously killed on his wedding day, Manfred plans to divorce his wife and marry the promised bride himself. After much frightening supernatural intervention, Manfred surrenders his claims to Otranto; he and his wife then enter neighboring convents.
Conrad, the fifteen-year-old son of Manfred. On his wedding day, he is found crushed to death beneath a gigantic helmet.
Isabella, the daughter of the Marquis of Vicenza and the fiancée of Conrad. Manfred plans to marry her after Conrad’s death, but she escapes him with the aid of the true heir to Otranto, whom she marries after Manfred’s abdication.
Theodore, a young peasant and the true heir to Otranto. He is imprisoned and nearly executed by Manfred’s order, but with both human and supernatural aid he triumphs, marrying Isabella and becoming the new Prince of Otranto.
Matilda, Manfred’s daughter. She gives aid to Theodore. Learning that Theodore is in the chapel with a woman, the jealous Manfred goes there and stabs the woman, only to learn that he has killed his daughter Matilda.
Father Jerome, formerly prince of Falconara, now a priest. Called to give absolution to the condemned Theodore, he discovers that Theodore is his own son, born before he entered the Church.
The Marquis of Vicenza
The Marquis of Vicenza, Isabella’s father. Disguised as the Knight of the Gigantic Sabre, he comes to Otranto, bringing with him a huge sword carried by a hundred men. On its blade is written that only Manfred’s blood can atone for the wrongs done to the family of the true heir. By betrothing the Marquis to Matilda, Manfred gets his consent to his own marriage with Isabella; however, terrifying omens and warnings cause the Marquis to renounce Matilda.
Prince Alfonso the Good
Prince Alfonso the Good, formerly the ruler of Otranto. It is the helmet of his statue that crushes Conrad. His giant form appears to proclaim Theodore, the son of his daughter, heir to Otranto. He then ascends to Heaven.
Saint Nicholas, who receives Prince Alfonso into Heaven.