Trivia: The baby used in Michael and Kay's baby christening scene is Sofia Coppola, Francis Ford Coppola's daughter. Sofia later had a prominent role in Part III as Michael's daughter, Mary.
Trivia: In the scene where Vito is in the garden with his grandson, he puts a lemon (or an orange) peel in his mouth, and the kid looks scared. Well, the kid really is scared. Marlon Brando improvised that, and the kid wasn't expecting it.
Trivia: Marlon Brando won a Best Actor Oscar for his role as Vito Corleone. Robert DeNiro, who played the role via flashbacks in Part II, won a Best Supporting Actor Oscar. They remain the only two actors to win Oscars for playing the same character.
Trivia: Johnny Fontaine was envisioned by Coppola as a young Sinatra, and was played by singer Al Martino. Martino didn't have much acting experience and was having difficulties getting his expressions and emotions right when the camera was on him. So, when he is in the office with the Godfather, the reason the camera is so often at his back is because he felt uncomfortable and unable to do the scene with the camera focused directly on him.
Trivia: During the shoot of the movie, many people were unhappy about the quality of acting Pacino was giving. They thought he was showing the character as dumb and slow-witted. It wasn't until the scene of the Sollozo murder, on the third and fourth day of shooting, that the big heads at Paramount saw "quality acting" on Pacino's part. However, Pacino was still not highly regarded until the Godfather became a big hit, and Coppola was criticized immensely, and was threatened to be fired for his cast choices and the manner in which he was filming the movie.
Trivia: The people at Paramount weren't impressed with Al Pacino's screen test, and kept urging Coppola to hire someone else to do the part. At one point, James Caan was favored for the part, even though he had already auditioned for the role of Sonny.
Trivia: The scene in the beginning where Marlon Brando is giving instructions (some involving violence) while petting the cat was somewhat improvised. It was Brando's idea to hold and pet the cat during the scene, to show both his character's violent and kind sides.
Trivia: Originally the character of Connie was supposed to be played by someone Coppola called "plain looking, the daughter of a big-shot who is only married off because she's the daughter of some big Mafioso guy". When they couldn't find an actress, Talia Shire, Coppola's sister, got the part, even though Coppola thought she was too beautiful and said "C'mon, look at her. Who wouldn't want to marry her?"
Trivia: In the scene outside the hospital when Michael encounters Capt. McCluskey, the officer standing to the left of McCluskey, "Phil" is actually former legendary New York City police officer, Sonny Grosso. Grosso was the actual partner of Eddie Eagan, who was portrayed by Gene Hackman as Popeye Doyle in "The French Connection" (1971). Grosso's character, Buddy "Cloudy" Russo was played by Roy Scheider. Grosso went on to direct and produce numerous police dramas for TV (the best known is "NYPD Blue"), usually about the New York Police Department.
Trivia: The cat in the first scene that Don Corleone was holding was a stray that Marlon Brando found. The cat purred so loudly that it drowned out the lines from the other characters. They ended up having to re-record their voices.
Trivia: Surprisingly, the word "Mafia" does not appear in the screenplay once. Apparently, the Italian-American Civil Rights League had an agreement with the film's producer not to use the term "Mafia" in the film.
Trivia: The Godfather was roundly criticized by the Italian-American Civil Rights League for its stereotypical portrayal of Italians.
Trivia: Marlon Brando plays Vito Corleone, father of "Fredo" Corleone (John Cazale). In real life, Brando was only 11 years older than Cazale.
Trivia: The horse's head that was cut off and placed into Woltz's bed was real - it was from a slaughterhouse. They painted on the stripe and added the fake blood.
Trivia: Al Pacino's real-life grandfather was born in Corleone, Sicily, the same town that the fictional Vito Corleone, Michael's father, was born in and from where he adopted the family surname. As a child, Pacino's family called him "Sonny." That is the same nickname his on-screen brother, played by James Caan, was called. Revealed by Al Pacino on The Actor's Studio.
Trivia: When Luca Brasi goes to visit the Tattaglia's and is strangled, you can see his face turning slightly black due to strangulation. This effect was achieved by placing a type of translucent powder on the actor's face which tints black when it comes in contact with water. So while Luca Brasi was being strangled, a fine mist of water was sprayed over his face to trigger the colour change.
Trivia: Al Pacino and Diane Keaton actually fell in love during the shoot, and were a couple for quite some time.
Trivia: Although Coppola was advised not to talk to real Mafioso because they would never stop bugging him and it might change how he filmed the movie, James Caan did spend time with various Mafia heads, and got much of his character quirks, expressions and gestures from them.