Clint Eastwood was approached to play the role of Willard, but he turned it down. One of he reasons? The story was "too dark." Seriously, Clint? We've seen Million Dollar Baby and Mystic River. (Source)

Brando had failed to read either Heart of Darkness or the script for the film, for that matter. Coppola spent weeks discussing Heart of Darkness and his role with him, while production came to a halt and 900+ cast and crew members sat around probably trying not to get heat stroke or malaria. (Source)

At the end of the opening scene where Martin Sheen breaks a mirror and cuts his hand, he started sobbing and tried to attack director Coppola. Is that what they mean by "method acting"? (Source)

Dennis Hopper didn't have to do much acting to come across as a manic, rambling journalist. He said he was using pot, amphetamines, and LSD during much of the shoot. We're sure he just did it for his art. (Source)

Harrison Ford plays a character named Col. G. Lucas in Apocalypse Now—a clear homage to George Lucas, who was friends with Coppola and Milius. Lucas directed Ford as Han Solo in Star Wars, which made Ford's career. (Source)