Writer and director Sir Alan Parker claims that Robert De Niro's performance as Louis Cyphre was so eerie and realistic that he generally avoided him during his scenes, letting him just direct himself.
When Louis (Robert De Niro) blows salt from his egg onto the restaurant table, Harry Angel (Mickey Rourke) takes a pinch and throws it over his left shoulder. The superstition is that by doing so you blind the devil (or your evil angel).
Singer Johnny Favorite's real name is Liebling, which is commonly used in German for "sweetheart" or "darling" (or angel), but its secondary meaning is "favorite".
This film was the impetus for a feud between Robert De Niro and Mickey Rourke. The first and last time the actors worked together, neither has had many kind words for the other since. The feud apparently stems from De Niro refusing to talk to Rourke off-camera, feeling this would be detrimental to their scenes together. Rourke apparently took this personally, and hasn't been shy about publicly bad-mouthing De Niro since. This bad blood has endured for decades, and in 2019 (32 years after this films release), Rourke accused De Niro of blocking him from taking a role in the Martin Scorsese's The Irishman. Rourke once said about De Niro, "I don't look up to him no more; I look through him."
The line "How terrible is wisdom when it brings no profit to the wise" is drawn from Sophocles' "Oedipus The King".