Gene Hackman played a former N.S.A. Agent who is a surveillance expert in Enemy of the State (1998), and the images of his character in his younger days are taken directly from this film. Hackman's characters are so similar in both movies, fans have theorized that they may be the same person, but there is no evidence of this provided by the makers of either film.
The blue Mercedes limousine that Cindy Williams is sitting in near the end of the film was won by Francis Ford Coppola on a bet with Paramount Pictures. Coppola had complained about the station wagon he shared with five other passengers during the filming of The Godfather (1972). Studio executives told him that if The Godfather had grossed a certain amount, they would spring for a new car. After The Godfather became the highest grossing film of all time, Coppola and George Lucas went to a dealer and picked out the Mercedes, telling the salesman to bill Paramount Pictures.
Gene Hackman was a fit, good-looking relatively young man when Francis Ford Coppola cast him as Harry Caul. In order to personify Harry's weary, aging, and unhappy existence, Hackman grew a pathetic-looking mustache, wore ill-fitting glasses, and had a wardrobe picked out that was at least ten years out of date. Coppola specifically told Hackman he wanted Harry to look like a "nudnik", a Yiddish word referring to a person who is boring and a pest.
Gene Hackman's character was to have been named Harry Call, but a typing error led to his being named Harry Caul, and the name stuck because Coppola liked how the meaning of the word caul (a birth defect causing a membrane to surround the head) related to the character.
Harrison Ford's part was initially intended to be a small cameo, written as little more than an office assistant. Feeling that the character was one-dimensional, Ford decided to play him as gay, a risky choice in 1974, and personally purchased the loud green silk suit for nine hundred dollars (4,285 in 2015 dollars). Francis Ford Coppola was at first shocked by the outfit at rehearsals, but after discussing it with Ford, was so impressed with this interpretation, that he expanded the role into a supporting character, gave the character a name (Martin Stett) and had Production Designer Dean Tavoularis create an office that reflected the character's orientation.
Francis Ford Coppola noted in the DVD commentary that Hackman had a very difficult time adapting to the Harry Caul character, because it was so much unlike himself. Coppola says that Hackman was at the time an outgoing and approachable person who preferred casual clothes, whereas Caul was meant to be a socially awkward loner who wore a raincoat and out-of-style glasses. Coppola said that Hackman's efforts to tap into the character made the actor moody and irritable on-set, but otherwise Coppola got along well with his leading man.
In the original script, Harry Caul was the owner of the building in which he lived. There was a deleted scene where he had a meeting with the other tenants. One of the people there was Mrs. Evangelista. Now, we only know of her character when Caul speaks to her on the phone after she leaves him a birthday present.
On the DVD commentary, Francis Ford Coppola says he was shocked to learn that the film utilized the very same surveillance and wire-tapping equipment that members of the Nixon Administration used to spy on political opponents prior to the Watergate scandal. Coppola has said this is the reason the film gained part of the recognition it has received, but that this is entirely coincidental. Not only was the script completed in the mid 1960s (before the Nixon Administration came to power) but the spying equipment used in the film was discovered through research, and the use of technical advisers, and not, as many believed, by revelatory newspaper stories about the Watergate break-in. Coppola also noted that filming had been completed several months before the most revelatory Watergate stories broke in the press. Since the film was released to theaters just a few months before Richard Nixon resigned as President, Coppola felt that audiences interpreted the film to be a reaction to both the Watergate scandal and its fall-out.
The original cut was four and a half hours long. Most significant was a subplot of Harry dealing with his neighbors, who complain about the building's plumbing problems, unaware that Harry owns the building. Other scenes feature Harry consulting his lawyer (played by Abe Vigoda) about the apartment situation, and Harry convincing his teenaged niece (played by Mackenzie Phillips) not to run away from home.
Due to creative differences on this shoot, veteran Cinematographer Haskell Wexler was replaced by Director of Photography Bill Butler. According to Coppola, Wexler visualized the movie in the more romantic style of The Thomas Crown Affair (1968), while Coppola saw it more in the cinéma vérité style of Medium Cool (1969) (Wexler was cinematographer on the former, and directed the latter).
During the party in the warehouse, Bernie Moran (Allen Garfield) brags that twelve years before, he had recorded the calls of an unnamed Presidential candidate, and may have determined who won the election. This presumably would have been the 1960 election, when John F. Kennedy narrowly won the election over Richard Nixon, who was at the time of the movie's production in the middle of his own taping scandal, known as Watergate.
Francis Ford Coppola tried to get funding for the film and failed to interest any studio or other investors. It was only after The Godfather (1972) was a hit, that Paramount Pictures offered him the money for The Conversation. Coppola has said that if it wasn't for The Godfather, this movie would never have been made.
The meaning of Harry's last name, Caul, is a fetal membrane sometimes present at birth. This ties in strongly with both Harry's transparent rain jacket, which he wears for the majority of the film, and also the fact that Harry is occasionally viewed through a translucent sheet of plastic when threatened, such as by his rival during the party scene.
Despite winning the Palme d'Or at the Cannes Film Festival, the Best Director awards from the National Board of Review, the Kansas City Film Critics Circle Awards, and the National Society of Film Critics Awards, and receiving additional nominations at the Golden Globes, the BAFTAs and the Directors Guild of America, Francis Ford Coppola did not receive an Academy Award nomination for Best Director. However, Coppola did receive an Oscar nomination for directing The Godfather: Part II (1974) that same year, which he inevitably won. Academy rules at the time did not allow for a person to receive multiple nominations in certain categories within the same year. Both films, produced by Coppola, were nominated Best Picture however. He was also nominated for writing both films, Original Screenplay for The Conversation and Adapted Screenplay for The Godfather: Part II.
Despite being awarded Best Actor by the National Board of Review and Best Performance in a Foreign Film at the Sant Jordi Awards, and also receiving additional nominations for Best Actor at the New York Film Critics Circle Awards, the Golden Globes and the BAFTAs, Gene Hackman failed to receive an Academy Award nomination for his performance. To this day, critics, audiences, major film groups and publications consider this a notorious snub.
The trivia items below may give away important plot points.
In the last scene, where Harry tears apart his apartment, Francis Ford Coppola stated on the commentary that he has no idea where the bug is. Two ideas he mentioned were the saxophone strap, or that there was no bug, and Harry was delusional.
DIRECTOR_CAMEO(Francis Ford Coppola): When Harry Caul turns on the television in the Jack Tar Hotel to blot out the sound of the murder in the neighboring room, the broadcaster is Coppola talking about Richard Nixon and the Watergate scandal, itself triggered by a notorious piece of bugging.
The Jack Tar Hotel on Van Ness Avenue, site of the grisly murder scene, opened in 1960, and later became the Cathedral Hill Hotel in 1982. It was demolished in 2013, to be replaced by a hospital complex.