Lee Sternthal and Brian Klugman wrote the script back in 1999. As friends of Bradley Cooper before his The Hangover (2009) fame, they ask him to play the lead, he accepted then, and kept his word more than ten years later.
When Rory Jansen (Bradley Cooper) finds and reads The Old Man's (Jeremy Irons') manuscript, the first page shown on-screen is actually an excerpt from Ernest Hemingway's memoir, "A Moveable Feast", discussing one of his early short stories called "Up in Michigan". Nearly all of Hemingway's other early works were lost because the suitcase his wife had packed them in was stolen from a train in Paris when she left in unattended for a few minutes. The Old Man's story parallels this event.
Six of this film's cast members appeared in superhero-related properties: Bradley Cooper as Rocket Racoon in the Marvel Cinematic Universe; Zoe Saldana as Gamora in the Marvel Cinematic Universe; John Hannah as Holden Radcliffe in Agents Of S.H.I.E.L.D. (2013); Ben Barnes as Billy Russo in The Punisher (2017); Jeremy Irons as Alfred in the DC Extended Universe; J.K. Simmons as Commissioner Gordon in the DC Extended Universe, and as J. Jonah Jameson in Sam Raimi's Spider-Man Trilogy.