John Castle (born 14 January 1940) is an English actor. Castle has acted in theatre, film and television. He is known for his role as Agrippa Postumus in the BBC television adaptation of I, Claudius (1976) and for playing Geoffrey II, Duke of Brittany, in the film The Lion in Winter (1968). He also played Dr Carrasco as well as the prisoner called "The Duke" in the film Man of La Mancha (1972), and the villainous Paul McDagget in RoboCop 3 (1993).