 -- Believe it or not, 45 years ago today, "The Godfather" hit movie theaters across the United States.

The film, starring Marlon Brando and a then-unknown Al Pacino, went on to become one of Hollywood's most commercially successful -- and critically acclaimed -- films, eventually earning more than $245 million worldwide, according to Box Office Mojo.

It also racked up three Oscars: best actor for Brando, best adapted screenplay for Mario Puzo and Francis Ford Coppola, and the coveted best picture award.

"The Godfather" enjoyed such success that it spawned two sequels and is ranked by the American Film Institute as the third-best movie in American cinema. However, while much has been said about the making of the film, here are a few stories even the biggest fan might not know.

1. Coppola didn't want to direct it -- nor was he the studio's first choice: According to a book of interviews with Coppola, the director was not excited about the project at first, nor was the studio thrilled about him. Coppola said he was only offered the film after Richard Brooks and Costa Gavras turned it down, and that he couldn't get through the book because it seemed like "pretty cheap stuff." "Four or five months later, I was again offered the opportunity to work on it and by that time I was in dire financial straits with my own company in San Francisco so I read further," he said. "Then I got into what the book is really about: the story of the family, this father and his sons, and questions of power and succession, and I thought it was a terrific story if you could cut out all the other [lurid] stuff." Eventually, he worked on the screenplay with Puzo and "The Godfather" script was born.

2. Coppola fought to get the cast he wanted: Coppola once said that he was only permitted to cast Brando as godfather Vito Corleone after he shot an "incredible" screen test with the actor that wowed executives. Ultimately, Brando was only paid about $120,000 for his work.

Coppola also had to go to the mattresses, so to speak, for Pacino, who told The Washington Post that he was almost fired three times. Originally, the studio brass suggested James Caan, who was later cast as Sonny Corleone, to play the part, but Coppola couldn't imagine Michael that way. “[Pacino's] intelligence is what I noted first. He knows how to use his gifts,” Coppola said. “He uses what he has, this striking magnetic quality, this smoldering ambiance.”

3. Brando loved to improvise: Coppola told Playboy that Brando came up with a lot of the details that made Vito Corleone the dynamic character he was. "I told him at one point that I didn't know how to shoot his final scene, just before he dies. What could we do to make his playing with his grandson believable?" he said. "[Brando] said, 'Here's how I play with kids,' and took an orange peel, cut it into pieces that looked like fangs and slipped them into his mouth."

"I thought, 'What a ridiculous idea. Then suddenly I saw it: Of course! The godfather dies as a monster!" Coppola continued. "Once I'd seen him with orange peel fangs, I knew I could never shoot it any other way."

4. Nobody on set was confident the movie would be a hit: "If you'd checked with the crew while we were filming, they'd have said, 'The Godfather' was going to be the biggest disaster of all time," Coppola said in the Playboy interview. "'The French Connection came out while we were filming and people who'd seen the film and who saw 'The Godfather' rushes implied that our film was boring by comparison. There were rumors that I was going to be fired every day. I was trying to save money during that time, sacking out on Jimmy Caan's couch. A bad period for me."

5. One of the most quoted lines from the film was also improvised: Last year, The Hollywood Reporter obtained drafts of "The Godfather" script, revealing how certain lines came to be. "Leave the gun, take the cannoli," a statement uttered by Richard Castellano's Clemenza, was originally, "Leave the gun." According to the publication, Castellano said the line at the suggestion of real-life wife, Ardell Sheridan, who also played his spouse in the film.

6. The opening scene was inspired by "Patton": Coppola said in an interview with NPR that he was inspired to write the opening scene of the film after a screenwriter friend suggested he do something similar to what he'd done before with "Patton." "He says, 'You know, Francis, you did such a good opening on 'Patton,' that was such a striking opening for the 'Patton' movie, couldn't you do something more like that? Something more unusual, that kind of got you into it?" Coppola recalled. "After he left, I had the idea to begin in this way, with this very, very close shot of the supplicant undertaker, Bonasera, and then slowly reveal out of the darkness this -- the Don's studio as opposed to the brightly lit wedding scene. The various characters ... Brando himself, his son, Sonny, and what have you. And I rewrote the opening and added it to the screenplay."

7. John Cazale was an obvious choice for Fredo: "Godfather" casting director Fred Roos said in an interview for the documentary, "I Knew It Was You: Rediscovering John Cazale" that though it was tough to cast Fredo, once he saw John Cazale in the play "Line," he knew he'd found the right guy for the part. "He had the warmth and the gentleness. He had all the qualities that I hoped for in Fredo," said Coppola. "There was no hesitation to cast him."

8. Diane Keaton loved playing opposite Pacino: The New York Times excerpted part of Keaton's memoir in 2011, in which the actress gushed about playing Michael Corleone's wife, Kay. For her, the joy of the film was all about working with Pacino, whom she dated off-screen as well. “Poor Al, he never wanted it. Poor me, I never stopped insisting," she wrote.

9. The time period was up in the air: Coppola told NPR that though the producers wanted the movie to be set in the 1970s, he insisted that it remain true to the book, which takes place in the 1940s. "[The producers argued] if you make a movie during the contemporary period that the movie is being made, you don't have to have special cars, you don't have to have special costumes, you don't have to spend all of that money trying to create a period," he said. Ultimately, he got his way.

10. The ending of the movie was meant to be brutal: Coppola also told NPR that he thought about ending the movie with Kay lighting a candle at church for Michael, but then thought better of it. "She says, 'Did you [commit murder]?' and he says, 'No.' He lies to her. ... I just felt emotionally that when he -- that door gets closed on her just as the other, what they call caporegimes are kissing his hand, that that was the ending," he said. "To go to her lighting candles was anti-climactical [sic], so I ended it there."

It also summed up the film, the director added.

"When I make a movie I always have to have a theme, preferably in one word," he said. "When I made 'The Godfather' the theme was succession."