Interesting film and play. Playwright Osborne did not intend to add the character of the knight (serving as part chorus, part psychological alter-ego) but the idea apparently came from Julian Glover the actor who plays the part. Apparently Glover added the part in the stage version as well. And that character is fascinating. According to IMDb, Tom Baker made an uncredited appearance as Pope Leo. But that bit is never shown in the version I viewed. Director Guy Green extracts good performances from all the characters, especially Stacy Keach. And cinematographer Freddie Young adds his touch with interesting camera angles in crucial scenes.
Review of Luther
