Opening in theaters this weekend, the new biopic Jackie takes on the myth of America’s Camelot in the moment of its fall, as First Lady Jackie Kennedy loses her husband, her home, her hero, and her illusions all in one fateful pull of Lee Harvey Oswald’s trigger. Chilean director Pablo Larraín uses an outsider’s eye to depict not only the familiar myth of the Kennedy years, but also the often unaddressed uncanniness of Jackie Kennedy. Though there have been movie Jackies before, never has there been a film so fixated on her insane baby voice, her beautiful blank mask of a face, or her deliciously campy love of home décor. And who better to lead us into Jackie’s collapsing fairy tale than Oscar winner Natalie Portman — herself the adult–child bride of a generation?

Natalie Portman is one of America’s most well-respected actors, having built her career for over two decades as a remarkably poised star whose worst scandal is probably a series of embarrassing-but-hardly-incriminating emails with Jonathan Safran Foer. But for all her placidity as a celebrity, as a performer, Portman’s presence mirrors Jackie Kennedy’s unsettling mixture of maturity and precociousness, and this has been true from the very first time she graced the screen in Luc Besson’s assassin thriller Leon: The Professional. Though Jean Reno had the title role, most of the film’s hype was built up around Portman as Mathilda, the child hell-bent on murder, whose character is balanced on the boundary between girlhood and teenhood as if on the blade of a knife. With Portman flitting coquettishly around her decades-older costar, it’s a film that only a French filmmaker could get away with making, and Leon was a cult film hit. From the creepy spectacle were born a thousand pervy Halloween costumes — hi Rooney Mara, hello Zoe Kravitz — and in Portman, one lifelong movie star.

Portman was inundated with offers after Leon, and her choices following that initial brush with stardom were telling, exposing both Portman’s interests as a young artist and the potentially exploitative way she was perceived by the industry. Tim Burton passed the wide-eyed dark-child baton from his former collaborator Winona Ryder to the young Portman with Mars Attacks!, Michael Mann cast Portman as Al Pacino’s suicidal stepdaughter in the crime drama Heat, and for her one pleasant family film, Beautiful Girls, Portman played the sweet and self-described “older than her years” girl-next-door who tempts Timothy Hutton with her adolescent crush. Even as a teen, Portman hovered somewhere in the in-between, mothering her mom Susan Sarandon in Anywhere But Here, yet still not mature enough to face real motherhood outside the utopic bubble of the local Walmart in Where the Heart Is.

By now, Natalie Portman has become such a Vogue-approved, Oscar-confirmed institution that it can be uncomfortable to recall the breathless Brooke Shields–esque hype that surrounded her when she first debuted. But if retracing the steps of Portman’s ascendence is a reminder of the inappropriate attentions of Hollywood’s starmaking machine, watching those first few Portman performances has a second degree of interest that can only be attributed to Portman’s own artistic development. Most performers tend to shed their child personas completely once they age into new roles — Natalie Wood rebelled with good cause from her start as a dubious Santa-denier, Drew Barrymore’s bad-girl phase broke her out of E.T. fame, and Scarlett Johansson went from horse whisperer to man-eater — but Natalie Portman has never totally ditched the persona she built as an adolescent. Where she was once famous for playing an oddly sexualized grown-up child, as an adult, her powers as a performer are never greater than when she’s playing a oddly sexualized, childlike grown-up.

As Portman began the transition to those quasi-adult roles, George Lucas flipped the script for Star Wars by casting the barely legal Portman as the elder love interest to the young Anakin Skywalker, who sprouts from child prodigy to leading man over the course of two films. Meanwhile, Mike Nichols brought Portman in to anchor the quartet in Closer as a stripper with a heart of gold and — surprise! — wisdom beyond her years. Wes Anderson eventually got onboard, too, bringing Portman into his dollhouse worlds as the most covetable grilled-cheese-eating doll of all in The Darjeeling Limited. But of all of Portman’s “not a girl, not yet a woman” roles, the most memorable might be her turn in Zach Braff’s 2004 romantic comedy Garden State.

Though it was highly regarded by the Sundance set when it premiered, Garden State is by now correctly regarded as the worst movie of all time — yet it is often unacknowledged that of all the bad things happening in Garden State, Natalie Portman is intriguingly maybe the worst of all. She’s the Manic Pixie Dream Girl taken to its logical extreme, at once spastic and cutesy and unconvincing even as she is idealized by her man-baby costar and director. If part of the abject horror of watching the movie is inherent to a script that thinks meet-cutes should happen while dogs hump Zach Braff’s legs, it can’t be denied that Portman’s eagerness, her persistent freaky baby quality, only makes the spectacle more mesmerizing. To be sure, no actress could have saved Garden State from itself, but it’s Portman who takes the film from forgettably bad to operatically bad.

But if Garden State proved that the grand weirdness of Portman can easily swing into disaster, the very same freakishness paired with the right project, the right filmmaker, and the right moment can make for work that’s equally and operatically sublime. In 2011, Portman won an Oscar for her turn as a ballerina twirling on the brink of insanity in Darren Aronofsky’s Black Swan, her girlish voice alarming as she cries from inside a bathroom stall like a lost teen at the school dance, “He picked me, Mommy.”

Black Swan brought every element of Portman’s prior performances into focus, making the quasi-sexual undertones of her earlier work explicit by marrying the tawdry story of a maybe-virgin unhinged with everything that was already striking about Portman’s presence onscreen, from her diminutive frame to the void of her emotional presence. Black Swan became a hundred-million-dollar smash and a major pop culture touchstone of this decade, with Portman’s Nina Sayers as the demented, sexually repressed object of a mass cultural obsession. It’s an unusual niche Portman has found for herself, but if Peter Pan complexes are rare to encounter in women at the movies, and maybe even rarer to encounter in life, Portman has made herself an unshakable icon of women stuck in transition. With Jackie, it’s to this state of transition that Portman returns.

In the end, what’s interesting about Natalie Portman is that all of the qualities that make her popular as a celebrity — her beauty, her poise, her conservative style, her respectability — are exactly at odds with the qualities that make her great as a movie star. If on a magazine cover, Natalie Portman is easily glossed into her most palatably respectable image, onscreen what makes her potent are all the parts of her persona that are unpalatable — the line readings that raise the hairs on your arms, the unrecognizable emptiness that sometimes overtakes her pretty face. For all of Portman’s fame as a celebrity who inspires the best from the young girls who admire her, in the privacy of the movie theater Portman is free to become the spectral nightmare of what happens to those very same ambitious girls when they are unable to grow up.