John Milius’s original screenplay moved Joseph Conrad’s 1898 novella Heart of Darkness from colonial Africa to the heart of the Vietnam War in the late 1960s. Although Milius made drastic changes, he left the basic structure intact: a man travels upriver to face an evil genius and, along the way, must face his fears, his mortality, and the possibility that he will go slowly insane. Director Francis Ford Coppola in turn embellished Milius’s screenplay to make it more closely mirror Conrad’s book, cutting scenes, adding others, and demanding a great deal of improvisation from his actors. Milius and Coppola therefore shared the film’s screenwriting credit. Author Michael Herr, who wrote a notable collection of Vietnam War articles entitled Dispatches, also received a writing credit for penning the film’s narration.

In addition to switching the setting, Milius renamed or modified nearly all of Conrad’s characters (aside from Kurtz). Conrad’s protagonist, Marlow, a pensive sailor on a quest to meet the ostensibly great, multitalented thinker Kurtz, becomes Milius’s Army Captain Benjamin Willard, an emotionally scarred Special Forces operative on a classified mission to terminate Kurtz. Milius’s Kurtz was an outstanding military officer who has apparently gone crazy. As the film opens, he leads a small colony in Cambodia, relying on “unsound methods” for imperious control. Moreover, Kurtz as portrayed by actor Marlon Brando is drastically different from the Kurtz of Conrad’s novella. Brando’s portrayal was influenced by his own corpulent, imposing physical presence, which contrasted greatly with the appearance of the emaciated Kurtz in Heart of Darkness. Conrad’s Kurtz withers away in the jaws of the jungle; Brando’s Kurtz is broad and large, with an imposing, sinister presence. Coppola decided to shoot Brando from the waist up to give him the appearance of being enormous and superhumanly tall without seeming fat.

As both Marlow and Willard make journeys up their respective rivers, they witness unthinkable atrocities. In Marlow’s case, the scenes of torture and slavery can be attributed to European imperialism. Willard’s story, on the other hand, requires him frequently to participate in the atrocities himself, as they are part of the war he is fighting. Heart of Darkness is a searing indictment of imperialism. Apocalypse Now similarly indicts the American presence during the war in Vietnam, which is seen by its critics as yet another version of western imperialism. In both stories, operating beyond the constraints of civilized society for an extended period leads to insanity. Reality in the novella and film is transformed into a cloudy surreal landscape where what is moral is gapingly unclear, moral judgment is no longer possible, and the very nature of humanity is challenged.

Coppola and cinematographer Vittorio Storaro translate the updated novella beautifully onto the screen, playing out the novella’s titular darkness visually through shadows and light-dark contrast. Joseph Conrad’s vivid descriptions of the Congo jungle jump into the film in the tiger scene, as Chef and Willard cower under mammoth trees. The fog that pervades the novella also features prominently the film, most notably when Willard emerges from the river at the film’s climax.

Milius’s original screenplay was structured with narration, but this narration was discarded during filming. Sound engineer Walter Murch, however, added his own voiceover during sound editing, because he felt the film lacked structure. Eventually, Michael Herr, a journalist who spent a year in Vietnam, later publishing his writing as Dispatches, was brought on to replace Murch’s narration. Herr’s work tells the story through Willard’s eyes and gives the film an intimacy and organization that otherwise would not exist. This narration humanizes Willard, making him more sympathetic and the story more comprehensible.