Joe Pesci appeared in one scene as a Mafia boss (Joseph Palmi) who, it is implied in the film, is a fictionalized version of Sam Giancana (in one scene, it is mentioned that Fidel Castro has seized "three of (Palmi's) casinos and thrown him out of (Cuba)". In fact, Castro did "nationalize" several Giancana-controlled casinos). The C.I.A. recruited Giancana for several assassination attempts on Castro.
Edward Wilson's (Matt Damon's) name is close to that of real-life C.I.A. Agent Edwin Wilson, who was involved in one of the most controversial episodes in the agency's history. An ex-Marine and Korean War veteran, the real Ed Wilson left the C.I.A. and was subsequently jailed for supplying arms and ex-Green Beret mercenaries as trainers to Libyan terrorist training camps. Wilson always claimed he was acting on C.I.A. orders and gathering intelligence on their behalf, later being exonerated and freed when released documents proved the C.I.A. had lied about severing all links with Wilson before the events occurred. A former C.I.A. Officer, David Adler, was the lawyer who got Wilson's conviction overturned.
When Wilson and Hayes are standing in the lobby of the under-construction C.I.A. Headquarters talking about the quote on the wall, Edwards asks what it means. Hayes replies "That's classified". The reply was appropriate, considering this would come to be known as the Wall of Honor, where undercover C.I.A. Agents, killed while on a mission would be honored only by a single star carved into the wall. There would be no names mentioned, because their work is classified.
Phillip Allen (William Hurt) is partly based on Allen Dulles, O.S.S. operative, and later C.I.A. Director during the Bay of Pigs invasion. Contrary to popular belief, President John F. Kennedy was fascinated with the world of espionage and unconventional warfare, granting the U.S. Special Forces their trademark Green Berets, while his enthusiasm for the James Bond novels helped to popularize them. However, during the C.I.A.'s Bay of Pigs operation he refused to allow overt military support for the mission, and severely limited the number of air strikes allowed to be flown by the C.I.A.'s own aircraft, for fear of revealing the U.S. Government's role. Both decisions are widely considered to have doomed the entire enterprise to failure from the start. Ironically, Allen Dulles was appointed to the Warren Commission investigating the assassination of President Kennedy, Dulles' former boss. Kennedy had fired Allen Dulles as head of the C.I.A.
Robert De Niro had a deal with Leonardo DiCaprio, who was interested in playing the film's protagonist Edward Wilson. De Niro planned to shoot the movie in the fall of 2004, but DiCaprio couldn't do it then, because he was making The Departed (2006) for Martin Scorsese. The role ultimately went to Matt Damon, who played DiCaprio's antagonist in The Departed (2006). Both movies were nominated for Oscars.
Eric Roth penned the screenplay in 1994 for Francis Ford Coppola and Columbia Pictures. Coppola left the project because, he said, he could not relate to the characters, finding them "unemotional", (although he retained a credit as co-Executive Producer).
The filming location of the Deer Island Club was Great Camp Sagamore on Raquette Lake in the Adirondacks. Sagamore was built by prominent designer and developer William West Durant, and is a notable example of the Gilded Age Adirondack Great Camp architecture. It was the summer retreat of the Vanderbilt family. The Sagamore interior proved to be too small to accommodate the entire film production crew, so a replica was constructed in New York City.
Two references to "Cardinal" are made in the movie, once in the beginning when the comment that "Cardinal is interested" is made by Ray Brocco and once at the end when Edward Wilson says that "it's a cardinal rule to be generous in a democracy". "Cardinal" was the code name of a high level American spy in the Soviet Union in Tom Clancy's novel The Cardinal of the Kremlin.
Wayne Wang was set to direct, but management changes at Columbia ended Wang's involvement, and Philip Kaufman was the next person set to direct, but he eventually left the project. When it moved to MGM, John Frankenheimer signed on to make the movie and wanted Robert De Niro to star. Unfortunately, Frankenheimer died in 2002, and at the same time, De Niro was developing his own spy story.
The trivia items below may give away important plot points.
Archy Cummings (Billy Crudup) was partly based on real-life British traitor Kim Philby, who attended Cambridge University, rose through the ranks of British Intelligence, and subsequently was discovered to be a Soviet spy. He later fled to Moscow, where he lived out the rest of his life. The movie reflects this, having Wilson speaking by phone to Cummings, who is in the Soviet Union.
Dr. Fredericks (Michael Gambon) was partly inspired by Alan Turing, a British mathematician who helped to crack the German "Enigma" code during World War II, and who is considered one of the founders of modern computer science. In 1952, Turing was expelled from the British Secret Service after being prosecuted for his homosexual affairs. In 1954, he died after eating a cyanide-laced apple, but it is unknown if he was murdered or committed suicide.
They give the "real" Valentin liquid LSD, which causes him to go crazy, ultimately restating that he is, indeed, Valentin Mironov, before committing suicide by jumping through the glass window. This is a reference to a real event wherein Frank Olson, a U.S. Army scientist, died in a similar way in 1953, allegedly as a result of his unwitting participation in LSD experiments, which were part of the C.I.A.'s "MKULTRA" program.
As previously mentioned there are two references to Cardinal; one in the beginning and one in the end. Both instances involve the exchange of a dollar. In the end, Edward's line regarding a "cardinal rule" could imply that Ulysses' bodyguard is in fact "Cardinal", a member of the K.G.B. and spy for the West.