Two maverick bad boys (actually, they were nice, normal people), Mario Puzo and Francis Ford Coppola, wrote the screenplay, based off Puzo's smash success of a novel (originally entitled Mafia before he changed it to The Godfather). But the road to the eventual movie masterpiece was a long and winding one.

Puzo wrote his book based partly off conversations with actual mobsters in Las Vegas—though he himself was never mafia-connected (granted, he did dig himself out of massive gambling debts by writing the book). The novel became a hit, and Paramount was all over it. Finally, after being signed to direct, Coppola began adapting and re-writing the script with Puzo.

Initially, however, Coppola wasn't a huge fan of the book itself: He didn't like the gratuitous sex scenes. But, despite these reservations, he ended up agreeing to team with Puzo. (Puzo would later go on to write the script for Superman II, commonly considered the best of the Superman movies, by the way.) Although he hadn't vibed with Puzo's book, Coppola found that he actually liked Puzo the man—they ended up working well together. They were able to craft a vision of organized crime in America and its strange and illicit re-working of the American Dream.

For more, check out this article in Vanity Fair.