Michael Douglas, producer

My father, Kirk, had acquired the rights to Ken Kesey’s novel in the early 1960s and developed it into a Broadway play, with him playing the lead character, RP McMurphy. He tried for years to turn it into a film, but it never got any momentum. Meanwhile, I was at university in Santa Barbara and was very politically active, what with the Vietnam war going on. I loved the book: it was a brilliantly conceived story of one man against the system. I had never thought about producing, but told my dad: “Let me run with this.”

Our first screenwriter, Lawrence Hauben, introduced me to the work of Miloš Forman. His 1967 film The Firemen’s Ball had the sort of qualities we were looking for: it took place in one enclosed situation, with a plethora of unique characters he had the ability to juggle. At the time, Miloš was living in the Chelsea Hotel in New York. He had apparently had a breakdown and never left the building – rumours were he would confide in a Czech friend while lying in bed, and then the friend would go out and see a psychiatrist on his behalf. But he flew to California to see us. Unlike the other directors we saw, who kept their cards close to their chest, he went through the script page by page and told us what he would do.

My producing partner, Saul Zaentz – the owner of Fantasy Records and a voracious reader – felt an affinity with Kesey. After Larry and I made a first attempt, Saul asked Kesey to write a screenplay and promised him a piece of the action. But like a lot of novelists trying to adapt their own material, it didn’t work out. We fell out with him after that. It was our only longstanding, painful issue. We got in to a financial dispute – it was silly, but maybe it was his way of defending his ego.

Hal Ashby, who had been in the early running for director, suggested Jack Nicholson for McMurphy. It was difficult to see at first, because he’d never played anyone like that before. We were delayed for about six months because of Jack’s schedule, but that turned out to be a great blessing: it gave us the chance to get the ensemble right.

Danny DeVito, who was my oldest friend and my roommate back in the late 60s, had played Martini, one of the patients in the psychiatric hospital, in the 1971 off-Broadway production, so he was the first to be cast. I found Will Sampson, who played Chief Bromden, through a used car dealer from Oregon who I’d sat next to on a plane. It turned out his dad was a Native American agent and he sold a lot of cars to them. I said we were looking for a big guy to play the chief and, six months later, got a call: “Michael, the biggest sonofabitch Indian came in the other day!”

The other insane decision Saul and I made was to shoot the film in an actual mental hospital in Oregon in January, when it gets dark at three in the afternoon. It was certainly a risk on the part of the hospital’s director, Dean Brooks, who ended up playing Jack’s supervisor in the film. He wanted to incorporate his patients into the crew. We ended up with a number of them working in different departments. I didn’t realise until later that many of them were criminally insane. We had an arsonist working in the art department. Dean identified a patient for each of the actors to shadow and some of the cast even slept on the wards at night.

Jack encouraged everyone to bring their A-game. When you look at that baseball scene, with him rallying all the patients to watch the game on TV, that’s just his inherent nature. But because Miloš never allows his actors to see the day’s filming, Jack was beginning to wonder about his performance. The cast was beginning to lose a little confidence in Miloš, and [cinematographer] Haskell Wexler, who wanted a directing career, was playing to those doubts a bit. I said to Miloš: “You’ve got to show Jack something.” So he did and everyone realised the film was in great shape. I had to fire Haskell shortly afterwards: it was either him or Miloš.

We went over-budget and over-schedule, but Saul had the courage to finance it beyond the initial estimate of $2m. It ended up at just over $4m. His partners accused me of taking him for a ride. But we knew we had a film – there wasn’t a false moment. When we went to the major studios to get a distributor, they all turned down what became a nine-time Oscar-nominated film that won best picture, director, actor, actress and screenplay. A lot more mentally ill people started coming out of the closet after that. The film allowed them to be seen as human beings.

Louise Fletcher, actor

I had an 11-year layoff from acting, having a wonderful time being a mother and housewife. But I ended up in Thieves Like Us, a Robert Altman film. When Miloš watched it to assess Shelley Duvall for a role in Cuckoo’s Nest, he asked who I was. It took four or five meetings, over a year, to convince him to let me play Nurse Ratched. I learned later they had offered it to other movie stars who turned them down.

So, on 4 January 1975, I turned up in Oregon for a week’s rehearsal, which was invaluable. We watched the patients in their daily routine and went to group therapy. Jack and I watched electroconvulsive shock therapy one morning at 6am – that was heavy. Making Ratched a human being was no small feat. You know nothing about her history, unlike McMurphy. I didn’t want to make her a monster – I wanted to make her believable as a real person in those circumstances. I drew on the misuse of power, a prominent issue in those times with Nixon having been forced to resign. I saw very clearly how people can believe that they’re doing good and they know best.

I had no makeup – just Vaseline on my lips and this crazy hairdo. I had to work within certain confines, but did a lot of improvising. And things would just happen organically. The great thing was that there were three cameras for the group therapy scenes, which was an unusual set-up. Normally they’d do a shot, then a reverse shot, but Miloš did them all at once, and it made a huge difference. Whenever Jack or another patient did something unexpected, like a blush, it was captured.

Jack asked me early on what Ratched’s first name was. I told him Mildred, which is what I’d made up. A few weeks later, we were filming McMurphy coming back from electroconvulsive shock therapy and pretending to be a zombie. Then he looks at me and says: “Hello, Mildred.” I was so shocked that my face turned red. It’s my favourite moment.

Towards the end, I was sick of all the constrictions to do with playing Nurse Ratched, right down to her tight clothes. I had stopped socialising with the cast because it wasn’t good for the role. They were having a lot of fun every night and I was jealous. I thought: “What can I get them as a goodbye present?” So one lunchtime, I asked the photographer to meet me in the ward. In one scene, which later got cut, McMurphy comes to breakfast wearing nothing but a pair of silky black boxer shorts with a whale embroidered on them. I put those on, with nothing on top, then pulled on my nurse’s shoes and hat and re-enacted that Betty Grable wartime poster, looking over my shoulder. I gave them all a print and signed it: “Mildred.”

The Oscars were wonderful. I didn’t think I was going to win, but I wrote a speech anyway. I didn’t tell anyone about signing “Thank you” to my parents, who are deaf, at the end, though. It was kind of scary for a year or two after: people would stop me at airports and tell me how much they hated me. Now I’m on all the best villain ever lists, alongside Anthony Hopkins for Hannibal Lecter. He’s usually No 1.

• One Flew Over the Cuckoo’s Nest is at BFI Southbank, London, and cinemas UK-wide from 14 April. Michael Douglas stars in Unlocked, out 5 May.