The character played by Christopher Reeve in the film is a composite of two different people: in Kazuo Ishiguro's novel, Stevens' new employer is an American by the name of Farraday, and has nothing to do with Mr. Lewis, the Senator.
Anthony Hopkins, as a guest on the TV show Inside the Actors Studio (1994), said that he got tips on how to play a butler from a real-life butler, Cyril Dickman who served for 50 years at Buckingham Palace. The butler said there was nothing to being a butler, really - when you're in the room it should be even more empty.
It was while shooting Mr. & Mrs. Bridge (1990) in Kansas City that actor Remak Ramsay, who was reading "The Remains of the Day" while playing a part in the film, gave the book to James Ivory to read thinking that its subject and setting might intrigue Ivory.
The trivia item below may give away important plot points.
The original screenplay was written by Harold Pinter for Mike Nichols. A few of his scenes survived the rewrite after Columbia reassigned the film to Merchant-Ivory (after which Pinter insisted that his name be removed from the credits). One of these scenes, almost at the very end of the film, where Anthony Hopkins finally accepts his failures and cries in front of a total stranger, a retired butler, did not make the final cut. The scene appears in the deleted scenes special features of the 2001 DVD release.