Coppola's claim that Brando showed up completely unprepared is a MYTH

Francis claimed Marlon was grossly overweight when he was more around 35 lbs. overweight at 5′ 9″ and somewhere over 225 pounds (this is clear in the movie).

He claimed Brando hadn't read "Heart of Darkness" -- Joseph Conrad's novel on which the film was loosely based -- when actually Mar read the novel (he had multiple editions of it in his 4000-book library). He intentionally shaved his head to fit Conrad’s description of ivory trader Mr. Kurtz as “impressively bald.” To be fair, Coppola said in an interview that Mar didn't read the book or shave his head until the end of the first week. Which account is true? I don't know.

In any case, Brando prepared for the film by reading other materials: The real-life account of CIA operative Anthony Poshepny, who worked with the Laotian Hmong in the hills to combat the NVA and used psychological warfare tactics like dropping severed heads into enemy locations (https://en.wikipedia.org/wiki/Anthony_Poshepny); The Pentagon Papers that were available at the time (https://en.wikipedia.org/wiki/Pentagon_Papers); writings by philosopher Hannah Arendt and anthropologist James Frazer; “Hollow Men” by TS Eliot, which featured first-hand accounts of the American Vietnam mission; and more.

The fact is that Coppola relied heavily on Brando for the crucial last act of the film, as supported by letters between the two, audio tapes of their discussions and the testimony of screenplay reviser & narration writer Michael Herr and Coppola biographer Peter Cowie. Marlon actually concocted a lot of the brilliant lines of his character; this is something Brando was famous (or infamous) for doing with his characters on set.

If all this is so, why were we told otherwise? Simple: Francis required a scapegoat. At the time the director was world-renowned and had won 2 Academy Awards, but in the Philippines making "Apocalypse Now" he was in over his head, which was verified by the crew and the media (see the excellent documentary "Hearts of Darkness: A Filmmaker's Apocalypse" https://www.imdb.com/title/tt0102015/?ref_=nv_sr_srsg_0). You'll remember that Coppola famously said at Cannes that the production was akin to its topic, the Vietnam war, wherein they all slowly "went insane."

Brando as an easy target for Francis since he was an eccentric loner and not a fan of fame, notoriously choosing to exploit it for personal profit and social causes. Mar made $3.5 million for a total of about 25 minutes of screen time and Coppola likely resented it.

So Francis absolved himself thru Marlon. He knew that Hollywood begrudged Brando and would eat-up the tale while Brando wouldn't contest it. Marlon avoided an open altercation in favor of writing Francis in private to convey his displeasure over his scapegoating account of what went down (keep in mind that Coppola didn't know at the time that "Apocalypse Now" would go down as one of the greatest films ever made). Understandably, in Marlon's 1994 autobiography, "Songs My Mother Taught Me," he didn't speak very respectfully of Coppola. This is why.

For more details see this article https://www.huffpost.com/entry/brando-v-coppola-debunkin_b_5587675