For his role as Hobie Doyle, Alden Ehrenreich learned horseback riding, rope tricks, twirling guns, and playing the guitar. He has stated twirling the spaghetti, mimicking the lasso, was the hardest part of his role.
Dolph Lundgren has an uncredited (initially much longer and almost entirely deleted) cameo as the submarine Captain. Lundgren said that he was very honored to play the part, having never expected to be asked for a movie directed by Joel and Ethan Coen.
The Coen brothers had been brainstorming the story for a decade but never actually wrote anything. George Clooney, as a practical joke, announced 'Hail, Caesar!' as his next film at a press conference. The Coens received so much publicity over Clooney's statement that they were effectively forced to make the film for real.
The Coen Brothers considered casting one hundred-year-old character actor Norman Lloyd as Herbert Marcuse, but changed their mind due to a scene in which he would have to appear on a boat in rocking water.
The film's central character "Eddie Mannix" was based on the real studio executive E.J. Mannix, who served not only as a producer, but also as legendary "fixer" at MGM. One of his most lasting contributions to motion picture history is a ledger he kept at the studio listing the budget and income of every film made at MGM from 1924 to 1962. It resides in the Margaret Herrick Library at the Fairbanks Center for Motion Picture Study in Beverly Hills, California.