On a winding back road of Texas Hill Country, Shelley Duvall pulled over and lit another cigarette.

“How did you like Egypt?” she called out from the white Toyota 4Runner she spends most of her days in, and some nights, much to the chagrin of her partner, Dan Gilroy. The “Egypt” she referred to is an industrial site one passes on the way into the small town Ms. Duvall has called home for more than a decade, its piles of sand and gravel, glimpsed at speed, resembling the ancient pyramids.

She cracked a grin, revving the engine. “Next stop: Santa Fe!” she announced before vanishing down the road in a cloud of dust.

To follow Ms. Duvall, 74, on the road and in conversation, is to enter into powerfully imaginative realms. Stories that begin in a certain direction have a habit of taking the scenic route, and, occasionally, swerving excitingly off-piste. One minute she might be talking in depth about shooting the horror film “The Shining” or the high jinks from the cast on the “Popeye” set, and the next she’s recalling lyrics from songs — all while retrieving crumpled headshots and cast photographs from a Ziploc bag she keeps in the SUV’s glove compartment.

Because of health issues, including diabetes and an injured foot that has greatly impacted her mobility (“My left one, like that Daniel Day-Lewis movie,” she joked), Ms. Duvall often stays in her 4Runner, some days driving to local nature spots, catching up with people in town and visiting drive-throughs. The driver’s seat is the only open space, as the interior is cluttered with takeout cartons and empty coffee cups.

For more than two decades, Ms. Duvall’s career was at a standstill. Her last film role had come in 2002’s “Manna From Heaven,” after which she retired for reasons that have remained a mystery from a varied and, by most counts, successful career as both an actor and producer. Among the most common questions that show up when you search her name these days: What happened to Shelley Duvall? and Why did Shelley Duvall disappear?

This enduring curiosity is unsurprising: The very act of fading into obscurity, be it voluntary or forced, is at the heart of the “Hollywood recluse” trope, which is used to tragic effect in classic movies such as “Sunset Boulevard” and “Whatever Happened to Baby Jane?” and never ceases to intrigue.

It intrigues Shelley Duvall as well.

“I was a star; I had leading roles,” she said, solemnly shaking her head. She had parked in the town square for a takeout lunch — chicken salad, quiche and sweetened iced coffee, finished off with a drag of a Parliament. She lowered her voice. “People think it’s just aging, but it’s not. It’s violence.”

Prompted to explain “violence,” Ms. Duvall responded with a question:

“How would you feel if people were really nice, and then, suddenly, on a dime” — she snapped her fingers — “they turn on you? You would never believe it unless it happens to you. That’s why you get hurt, because you can’t really believe it’s true.”

“Everyone’s always interested in downfall stories,” said Mr. Gilroy, 76, her partner of more than 30 years, who helps her get in and out of her car and sometimes has to plead with her to come back into the house. His voice bore a tone of weariness in discussing the speculation and gossip that still surrounds Ms. Duvall, focusing not only on her mental health, but also her body.

“It’s all over the internet: ‘Look at her now’ and ‘You won’t believe what she looks like now.’ Every celebrity gets that treatment.”

He has reason to feel weary, of course: In 2016, Ms. Duvall was a guest on the daytime talk show “Dr. Phil,” with the rare television appearance proving to be personally disastrous. Still controversial eight years later, the episode, filmed at the local Best Western without Mr. Gilroy’s knowledge — “I found out days later from people in town that it had happened,” Mr. Gilroy said — showed Ms. Duvall in a state of distress.

“I’m very sick. I need help,” Ms. Duvall told Dr. Phil in one clip. He responded: “Well, that’s why I’m here.”

The episode was titled “A Hollywood Star’s Descent Into Mental Illness: Saving The Shining’s Shelley Duvall.” Wide-eyed, Ms. Duvall went on to utter a slew of bizarre statements, such as claiming to be receiving messages from a “shapeshifting” Robin Williams, who had died two years before, and talking about malevolent forces who were out to do her harm. While the show’s stated aim was one of empowerment and destigmatizing mental illness, many, including Stanley Kubrick’s daughter Vivian, publicly criticized the show for being exploitative and sensationalist.

Although the episode never aired in full, the damage was done. It led to questions regarding her mental state, and she withdrew further into herself.

“It did nothing for her,” said Mr. Gilroy, of the show. “It just put her on the map as an oddity.”

‘The Female Buster Keaton’

Ms. Duvall, born in Fort Worth in 1949 to Robert and Bobbie Duvall, who worked in law and real estate, had a performative streak. Growing up the oldest and only daughter of four children, Ms. Duvall had always been headstrong.

“I was in a choir once and the person next to me was singing really off key and I couldn’t stand it. I had to ask to stand near someone else,” she said with a smile.

While Ms. Duvall lacked formal training, or certain qualities you might expect of a traditional leading lady, her rawness worked to her advantage. For one thing, she didn’t look or carry herself like a classic Hollywood starlet. She brought an energy to her roles that jarred with the studied naturalism that was the acting style at the time, her voice had a beguiling singsong quality to it, and she had a talent for improvisation.

While these days it is rare for actresses to show their age on or off screen, Ms. Duvall has aged naturally. With her fine gray hair coaxed into three bright scrunchies on top of her head, and, in a faded pink tracksuit, the Ms. Duvall of today cuts a strikingly different figure to the waif who bewitched filmgoers throughout the ’70s and ’80s.

But her smile is still expressive and kind, her wispy eyebrows often arching to emphasize certain points, to make the listener laugh and win them over. She has an almost cartoonish physicality, with doleful eyes and a goofy humor. This was the woman who once dated Paul Simon and Ringo Starr and worked with some of the era’s most famous directors: Robert Altman, Terry Gilliam and Mr. Kubrick, among them. Her sharp fashion sense — miniskirts, winklepickers, spidery eyelashes — earned her the nickname “Texas Twiggy.”

What made her so captivating then (the film critic Pauline Kael called her the “female Buster Keaton”) still exists: a raw honesty, an intuitive quality and a winsome Texas drawl.

“I remember, on ‘Saturday Night Live,’” Mr. Gilroy said, “they did a joke in which they were in some kind of room and you could hear the neighbors right through the wall, and one of the lines was, “These walls are thinner than Shelley Duvall!”

Her disappearance wasn’t, as it had been rumored, born of a protracted breakdown caused years before by her treatment on the set of “The Shining.” In fact, she continues to have only good things to say about that intense yearlong shoot in London and her admiration for Mr. Kubrick. Instead, the pause may be more accurately, though not definitively, attributed to the emotional impact of two events: the 1994 Northridge earthquake, which damaged her Los Angeles home, and the stressful toll of one of her brothers falling ill, which prompted her return to her native Texas three decades ago.

It could also equally be attributed to the curse of fame: It isn’t enough to be famous; one must continuously stoke the fire. Leave it for too long, especially if you begin to “age out” as a woman in the industry, and a career will wane.

In 1982, two years after “The Shining” made her a household name, Ms. Duvall started her own production company, Platypus (and, later, another called Think Entertainment), creating television shows for children, most notably “Faerie Tale Theatre.” Each episode boasted an all-star cast: Robin Williams, Christopher Reeve, Carol Kane, Bud Cort, Bernadette Peters, and Mick Jagger among them. The overall effect was one of baroque fun, or as Time magazine proclaimed, it offered “a hip, witty twist to storybook classics.”

“It’s like being a captain of a ship — you have to steer it in the right direction,” she said of producing. Her eyes lit up as she spoke about that fertile creative time, and the painstaking levels of research she undertook for each project.

“I had great people to work with, and of course I got Robert Altman to direct an episode,” she said. “He was always there for me.”

Never intending to become an actor, Ms. Duvall said she owed her career to Mr. Altman, the acclaimed director who cast her in her first role in his 1970 dark comedy “Brewster McCloud,” after she met two of his producers at a party when she was 20.

“He was real fatherly,” she said of Mr. Altman. “Sometimes too much so. He was like the old lady who lived in the shoe, who had too many children she didn’t know what to do, you know?”

The pair became close friends and would go on to collaborate on seven movies including “Nashville,” “Thieves Like Us” (where, incidentally, Ms. Duvall picked up her smoking habit), “McCabe & Mrs. Miller,” “Popeye” and “3 Women,” for which Ms. Duvall won the 1977 Best Actress Award at Cannes.

“I thought: boy, if it’s this easy, why doesn’t everybody act?” she said.

‘I like the way you cry’

After more than two decades, Ms. Duvall is set to make a return to movies this spring in “The Forest Hills.”

Ms. Duvall plays Mama, the mother of Rico (Chiko Mendez), a man who, according to the film’s logline, is “tormented by nightmarish visions after enduring head trauma.” The film also features Edward Furlong (“Terminator 2”), another actor who has spent a long time away from the spotlight.

Taking her restricted mobility into consideration, the crew traveled to Texas from their main location in upstate New York on three occasions, so that Ms. Duvall could perform her scenes from home. There was a lot of technical problem-solving. For instance, her wheelchair, which Ms. Duvall uses when she isn’t in the car, became part of the story. When asked how she came to be involved in the project, Ms. Duvall shrugged: “I wanted to act again. And then this guy kept calling, and so I wound up doing it.”

If the crew had any qualms working with Ms. Duvall, they were immediately soothed. “She was able to bring her acting abilities to the table and deliver her lines and bring the character of Mama to life,” the director Scott Goldberg, for whom this will be his third feature, said on a recent phone call. “She was one hundred percent a natural. It was as if time never passed.”

Ms. Duvall mused: “If you ever do a horror film, other horror films are going to come to you, no matter what you do.”

“The Shining,” though, would become one of the most iconic in the genre. Mr. Kubrick was inspired to cast her in his film after seeing her in Mr. Altman’s “3 Women.”

“He said: ‘I like the way you cry.’”

Though the shoot was grueling — Mr. Kubrick is known for demanding his actors do hundreds of takes for each scene — she has fond memories of the experience. Mr. Kubrick and Ms. Duvall would play chess during breaks, and the crew would sit around smoking cigarettes and eating Big Macs.

She recalled how shocked she was when she saw the final cut. “There were scenes I didn’t watch being filmed. You know that scene with the two little girls at the end of the hallway, and then they step apart? And you see what’s behind them? That was scary, very scary.”

Critics at the time picked her performance apart, and she was nominated for a Razzie award for worst actress. But something in the authenticity of her reactions, her otherworldliness, resonated with audiences.

“You forget that she’s acting,” said Nathan Abrams, a professor of film studies at Bangor University and the co-author of a new biography on Mr. Kubrick. “It’s a fantastic performance. Shelley goes through a range of emotions: loving mother, doting wife, and then that scared partner. I think Kubrick clearly saw that ability in that range, and then coached that performance out of her.”

“When it comes to horror you really have to strip away everything, and give your soul and really be present,” said the actress Felissa Rose, Ms. Duvall’s co-star in “The Forest Hills,” who is best known for starring in the 1983 cult slasher classic “Sleepaway Camp.”

Ms. Rose added: “We’re talking about people who are truly ready to unleash their truth, and those people are fun to watch — and that’s exactly what she gave in ‘The Shining.’”

When asked for her thoughts about Ms. Duvall’s disappearance, Ms. Rose said, “A lot of people in this industry put up walls, or say, ‘You’re Teflon!’ or ‘You have a thick skin!’ you know, have a facade. And she walked in with authenticity and truth, and that’s hard.”

This vulnerability and openness, perhaps even naiveté, made her particularly susceptible to mistreatment. Into the ’80s, the types of roles Ms. Duvall was getting shifted. No longer the young, willowy ingénue, she was cast in more mature roles. In a sense she had moved on, by producing television shows, with built-in acting opportunities within those.

Following the success of her shows “Faerie Tale Theatre” and “Bedtime Stories,” she produced the 1990 Disney television musical “Mother Goose Rock ‘n’ Rhyme,” where she met and fell in love with Mr. Gilroy, a musician and member of the group Breakfast Club, who composed and performed some of the soundtrack.

The couple has lived in a rustic one-story house surrounded by fields for over a decade. “It’s a little oasis for us,” Mr. Gilroy said.

Indeed, it’s an isolated but serene setup: Mr. Gilroy’s paintings-in-progress stand on easels in the living room, while old framed photographs of Mr. Gilroy and Ms. Duvall smiling affectionately at each other glint on the mantle above the stone fireplace. Scattered around are piles of fan mail.

“It was great, all those years in L.A., really terrific,” said Mr. Gilroy. “And when we moved, after the earthquake, it was terrific in Texas. Things went downhill when she started becoming afraid of things, maybe didn’t want to work. It’s really hard to pin it on any one thing.”

Ms. Duvall, once praised for her great imagination, was now being haunted by it. “She became paranoid and just kind of delusional, thinking she was being attacked,” said Mr. Gilroy. “She tried to make calls to the F.B.I., and asked our neighbor to protect us.”

“It was just shocking that, suddenly, from normal, it went south like that,” he added.

‘Hello, I’m Shelley Duvall’

Despite her decades’ long disappearance, Ms. Duvall’s filmography has thrived. Instagram users regularly source new Shelley material from an apparently bottomless archival trove.

“Hello, I’m Shelley Duvall,” a line Ms. Duvall would utter as she presented each episode of “Faerie Tale Theatre,” is sampled ad nauseam in posts. Yet there are no books, no documentaries, no star on the Walk of Fame. Seemingly dismissed and forgotten by the filmmaking establishment, she has become a cult figure for the quirky, the alternative and the misunderstood — and they seem to want to protect her, and her legacy, making their own podcasts and films.

“I think she’s pretty relatable, like, she kind of came from nothing,” said Sarah Lukowski, 23, an Austin-based copywriter who runs a popular Instagram account devoted to all things Shelley Duvall.

Ms. Lukowski became enthralled with Ms. Duvall after watching “The Shining” for the first time in 2016. “It’s her unique look: the big eyes and oversized teeth and her offbeat personality — she reminded me a lot of myself.”

The pair now meet up every few months and Ms. Lukowski has become friends with fellow Shelley fans too.

“She was such an enigmatic force,” Ms. Lukowski continued. “I mean there are actors today like Anya Taylor-Joy and Mia Goth who have similar features and acting styles, but there’ll never be another Shelley, you know?”

This wave of new fans is something Ms. Duvall finds hard to fathom. She seems to straddle between disappointment and a sense of betrayal toward an industry to which she gave so much of herself and yet still misses her old life in Hollywood, when she and Mr. Gilroy hobnobbed with famous friends.

She relishes discussing her career highs, but does not elaborate when prompted to talk about the more troubled aspects of her past.

“That’s so great, look at that,” she said, pointing to a small dog being carted along the sidewalk in a baby stroller. “Thank goodness for comic relief, right? Do you know that all nine dogs I brought down from L.A. died on that street over there?”

Pets have always been a big part of Ms. Duvall’s life and she currently has three parrots, a few cats and a geriatric mutt called Puppy. Passing by a field of thin-looking donkeys on the way home, Ms. Duvall often stops to feed them a couple of slices of sandwich bread through the wire fence. Her innate connection to the natural world lends to a sense of wonderment.

As she drove home, Ms. Duvall’s hand would occasionally trail out of the window, holding a smoldering cigarette, motioning over to roadkill or comically snapping like a beak.

Sometimes she disappeared from view entirely.