Francis Ford Coppola was not the first choice to direct The Godfather, Paramount Studios wanted Sergio Leone, but he turned it down to concentrate on his own gangster movie Once Upon A Time in America. Next up was Peter Bogdanovich but he also knocked it back as he was working on What’s Up, Doc?. Coppola was eventually approached by producer Robert Evans, who wanted an Italian-American to direct the film.

As Coppola later recalled in an interview:

The Godfather was a very unappreciated movie when we were making it. They were very unhappy with it. They didn’t like the cast. They didn’t like the way I was shooting it. I was always on the verge of getting fired. So it was an extremely nightmarish experience. I had two little kids, and the third one was born during that. We lived in a little apartment, and I was basically frightened that they didn’t like it. They had as much as said that, so when it was all over I wasn’t at all confident that it was going to be successful, and that I’d ever get another job.

 

 
Coppola was considered a risk. He had made five movies, only one of which was a hit. He was also in debt to Warner Brothers from an overspend while producing THX 1138.

Paramount were still skeptical about Coppola’s ability and kept a standby director ready to replace him. The first argument between director and studio came over casting. Coppola had drawn up his own list of possible contenders, which the studio was also set against, in particular they did not like Coppola’s suggestion of Marlon Brando or Laurence Olivier for Vito Corleone.
 

 
Coppola wanted the world’s greatest actors for the main role, but the studio didn’t want Brando because he had a bad reputation for delaying film productions; while Olivier was supposedly too ill to film and turned the offer down.

Who the studio wanted was Ernest Borgnine, as he had the mix of rough-and-ready, and seemed like the kind of “family man” an audience would identify with.
 

 
For Michael Corleone, Coppola wanted (then mainly unknown) Al Pacino, but the studio wanted a name, a hit name like Robert Redford or Ryan O’Neal.

Michael was a good, strong role, and it attracted Martin Sheen, Jack Nicholson, Warren Beatty, Dustin Hoffman and James Caan to audition for the role, but Coppola threatened to quit unless Pacino was given it. The studio eventually conceded on the agreement that James Caan was cast as Sonny Corleone.

Again the lure of box office names led to considering Paul Newman and Steve McQueen for the role of lawyer Tom Hagen, but that eventually went to Robert Duvall.
 

 
Other stars who went up for roles include Anthony Perkins who auditioned for Sonny, while Mia Farrow auditioned for Kay. Meanwhile, Robert De Niro tried out for Michael, Sonny, Carlo, and Paulie. He eventually played the young Vito in The Godfather Part II.

This is Coppola’s original cast list, which contains many of the names who eventually appeared in the film.
 

 
Via Retronaut, FuckyeahDonCorleone and Julia Segal