One of the things that made The Godfather the success that it was the alchemy of the casting. Marlon Brando as the Godfather and the four sons and how that all worked together. Very different than how Paramount wanted the film to be cast. Originally they wanted Laurence Olivier to play the Godfather, and they wanted Robert Redford to play Michael. Because in the book Michael is described as not looking Italian, that he was a sport, genetic sport. And this, in fact, is true. The Normans invaded Sicily sometime in the 12th century, so there... there is a genetic strain in Sicily of this Norman Northern blood that occasionally pops up. So that's the concept behind, in the book, what Michael looked like. Francis didn't want to use that casting; he wanted Marlon Brando, and he wanted the people that he eventually got. James Caan as Sonny, Michael played by Al Pacino, Fredo played by John Cazale and Robert Duvall playing Tom Hagen, who was an adopted son.
There's... Looking at this film made me realise that in casting a film there's a weaving of fabric where you can think of one line of the fabric being what you might call vertical casting, which is, does that person resemble the person described in the text, whatever it is, the novel or the screenplay. And from a vertical point of view, Paramount was probably as right as anyone could be. Laurence Olivier is a great actor. He could play that part, and he could be made up to look even more like that part. And if you read the original novel, Robert Redford kind of does look like the Michael in the book.