If you had to list the iconic screen villains of the past century, a few names would immediately come to mind: Darth Vader, Hannibal Lecter, the Wicked Witch of the West, Norman Bates, the Joker. The characters we’ve collectively deemed pure evil make up a rogues’ gallery of serial killers, monsters, and cackling harpies. Any decent roster would have to include Nurse Ratched, of One Flew over the Cuckoo’s Nest, who manages to be as terrifying (and terrorizing) as the rest, without green skin or a taste for human liver.

But as far as dark hearts—or the totally heartless—go, is she really as bad as all that? Sure, she rules her wards as a petty tyrant, punishing miscreants with electroshock and lobotomies. But from our perspective in the mid-#MeToo, post-Lean In era, you could see her as an overzealous working woman, a frustrated bureaucrat trying to maintain professionalism in the face of one R. P. McMurphy, a rabble-rousing psychiatric patient who’s been convicted of assault and statutory rape. (He’s the hero.)

Ken Kesey’s 1962 novel was already considered a “nonconformists’ bible,” as Pauline Kael put it in The New Yorker, when Miloš Forman’s film was released in the fall of 1975, epitomizing a nation at war with itself. At its center are two opposing forces. Jack Nicholson’s McMurphy is a scoundrel, a madman, a trickster, a martyr—a symbol of the wild human spirit itching to break free. Nurse Ratched is everything he’s not: orderly, rule-bound, the banality of evil in a crisp white cap. Their escalating fight to the finish was the same one that had split America into two incompatible halves: the Establishment and the counterculture.

So nimbly did the movie capture its time—60s liberation doused with 70s vinegar—that it became one of only three films in Oscar history to win the Big Five, for best picture, director, screenplay, actor, and actress. (The other two are It Happened One Night and The Silence of the Lambs.) Barack Obama called it one of his favorite films, alongside Casablanca. While the movie cemented Nicholson as New Hollywood’s lovable rogue, something about his antagonist was so frightening, so Freudian, that it lifted her into the realm of icon. “Nurse Ratched’s soft, controlled voice and girlishly antiseptic manner always put you in the wrong; you can’t cut through the crap in her—it goes too deep,” Kael wrote. “And she’s too smart for you; she’s got all the protocol in the world on her side.”

Forty-three years later, she’s about to get a second look. Netflix recently won a bidding war for Ratched, an 18-episode series that will trace the character’s origin story, produced by Ryan Murphy and starring Sarah Paulson. One can imagine Murphy and Paulson giving her the same redeeming nuance they brought to Marcia Clark in The People v. O. J. Simpson: American Crime Story. Is Nurse Ratched a feminist anti-heroine waiting to happen? Or is she a monster? If the character still tugs at our curiosity, that’s in large part because of Louise Fletcher, the actress who gave Nurse Ratched the humanity she never had on the page—and in the process made her even scarier.

To understand how Fletcher—and Forman, who died this past April—made cinematic history, you have to start in the spring of 1960, with a 24-year-old former college wrestler named Ken Kesey. As a creative-writing student at Stanford, Kesey volunteered as a guinea pig in a government-funded study of the effects of psychoactive drugs such as LSD. Every Tuesday morning at eight, he would show up at Menlo Park Veterans Hospital, where a doctor would hand him pills and a shot of juice and keep him under observation. “Patients straggled by in the hall outside, their faces all ghastly confessions,” Kesey wrote later. Sometimes a nurse checked in, looking full of “painful business . . . This was not a person you could allow yourself to be naked in front of.”