In The Castle of Otranto, Theodore is the peasant who is revealed to be the true prince of Otranto.
Theodore first appears to be a low-born young man who recognizes that the gigantic helmet crushing Conrad is linked to the castle's supernatural prophecy. He helps Isabella escape Manfred, the desperate lord of Otranto, and is punished when Manfred suspects him of involvement in the strange events surrounding the castle.
The plot changes when Friar Jerome sees a distinctive mark on Theodore's body. Jerome recognizes him as his long-lost son and reveals that Theodore is of noble birth. His identity fulfills the prophecy that Otranto will pass from Manfred's family when the rightful owner has grown large enough to claim it.
Theodore later becomes prince of Otranto and marries Isabella after Matilda, Manfred's daughter, dies accidentally at her father's hand. Conrad is Manfred's dead son, Hippolita is Manfred's wife, and Manfred is the usurping ruler—not the true heir. Horace Walpole's 1764 novel is often regarded as the first Gothic novel, blending medieval romance, family secrets, prophecy, and supernatural spectacle.