Thanks to its emphasis on classical training and its intrinsically vibrant theater scene, the United Kingdom produces many actors who can command complete authenticity in historical film roles. John Castle is one such performer. He excelled as Geoffrey in the 1968 Oscar-winning film "The Lion in Winter", set in 12th-century England. He was entirely convincing as Postumus in the 1976 landmark BBC-TV series "I, Claudius". And he reteamed once again with his "Winter" co-star Peter O'Toole for 1972's "Man of La Mancha". Fans of the TV series "The Prisoner" will remember him for his single-episode work as Number Twelve. Early in his career, he also played Italian dictator Benito Mussolini on four installments of "Thirty-Minute Theater". For the 1986 U.K. TV series "Lost Empires", set in the 1910s world of British music halls, he was Nick Ollanton, and a production of "Little Lord Fauntleroy" in 1995 cast him as Havisham. In 2006, he guest starred on a pair of episodes of the BBC drama series "MI-5".