Nathan Fillion as Richard Edgar Castle/Richard Alexander Rodgers, a best-selling mystery writer. Plagued with writer's block after killing off his popular lead character, Derrick Storm, whom he no longer found inspiring, Castle finds himself involved in the case of a copycat killer recreating murder scenes from his novels. He discovers a new source of inspiration in Kate Beckett, the detective leading the investigation, so he uses his friendship with the mayor of New York to become involved in her investigations as a civilian consultant. He regularly uses his knowledge and talent to help solve murders, usually by taking evidence and assembling it into a narrative to explain their current case. He is twice-divorced and shares an apartment with his daughter and his mother. Earlier seasons of the show depict him as an immature womanizer; however, later seasons show a more mature and sensible side of him, albeit only slightly. His close working relationship with Beckett results in him falling in love with her. They get together in the start of season five. He proposes at the end of the fifth season, the two become engaged in season six, and they marry in the seventh season.