Rudolf Rassendyll is the main character in the novel "The Prisoner of Zenda," written by Anthony Hope. He is an Englishman who travels to the fictional European country of Ruritania and discovers he bears a striking resemblance to the imprisoned king, Rudolf V. Rassendyll becomes embroiled in a political intrigue when he is asked to impersonate the king to prevent a coup. His adventure involves themes of honor, bravery, and the complexities of identity as he navigates the challenges of royal life while trying to save the monarchy.