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).
Castle was born in Croydon, Surrey. He was educated at Brighton College and Trinity College, Dublin, and trained at the Royal Academy of Dramatic Art.
Castle's first appearance was as Westmoreland on stage in Henry V on 5 June 1964, at the Open Air Theatre, Regent's Park. His first Broadway theatre appearance was in February 1970, as Jos in the short-lived musical Georgy.
In 1967 he made his screen debut as the plotting Prince Geoffrey in the big-screen adaptation of The Lion in Winter. The role garnered him much praise and set him on his way as a supporting actor in London and Hollywood.
John Francis Castle (June 1, 1879 – April 13, 1929) was an outfielder in Major League Baseball. He played three games for the Philadelphia Phillies in 1910.