Mario Puzo had invented the term ‘The Godfather’ for the novel. It didn’t exist. That’s not all that was invented by Puzo. According to Francis Ford Coppola, who made the movie, the term “Don Corleone” is wrong. In Italian, addressing someone as “Don” is the same as addressing them as “Uncle” in English. Correct usage would be “Don Michael” or “Don Vito”. Coppola says that Mario Puzo, who couldn’t speak Italian, made up the idea of using “Don” with a person’s last name and it stuck, totally transcending The Godfather.
Source: Godfather Trivia
The Godfather was written by Mario Puzo. It was published in 1969.