Sarah Michelle Gellar in season five’s “The Gift.” Photo: 20thCentFox/Courtesy Everett

There are certain days that separate our lives into “befores” and “afters.” For me, one of those days is March 10, 1997. I was almost 8 years old, flipping channels after another day at my Christian private school, and I happened upon the first episode of Buffy the Vampire Slayer, “Welcome to the Hellmouth.” I was never sure what specifically sparked my interest, which would turn into a lifelong obsession with the series. Buffy the Vampire Slayer, the Joss Whedon series that premiered 20 years ago Friday, centers on the 16-year-old Buffy (played with finely tuned vulnerability and humor by Sarah Michelle Gellar) as she goes through the usual pains of growing up while also being burdened by her destiny: She’s part of a line of young women chosen to be vampire slayers. Rewatching the series as an adult, I realized why my preteen self fell so quickly for Buffy: the opening sequence.

The first few minutes are a simple twist on horror film tropes, which Buffy mined over the course of its seven seasons. It opens on an empty high school at night. The camera careens through the shadowy halls and classrooms, beneath neatly aligned desks. The quiet is broken by a young couple breaking in. Of course, it’s the woman you’re worried about at first. She’s a bundle of blonde anxiety, her eyes roving through the darkness. The man teases her nerves. “There’s no one here,” he assures her. “Are you sure?” she asks. Before he can react, she turns around to reveal a gruesome face and hideous fangs, marring the delicate looks that made us believe she was a victim just moments earlier. She’s actually a vampire, and he’s dinner.

It crystallizes what made Buffy so fresh 20 years ago and still fresh today. The series was at its best charting women in moments of fraught transition — between victim and monster, heroine and villain, girlhood and womanhood — and subverting our expectations along the way. And it’s Buffy, the wonderfully complex lead character, who communicates these ideas time and again.

The 1990s were full of feminist vanguards in genre fiction, from The X-Files’ focused Dana Scully to the aggressive and campily humorous Xena of Xena: Warrior Princess. I may no longer believe any show can be truly feminist (that’s too tricky a criterion to judge), but Buffy was one of the many things in my adolescence that sparked my interest in what it means to be a woman in the world and how necessary feminism is to our survival. Whedon’s interest in feminism was explicit, present in the show’s visual choices, dialogue, and the ways it played with genre.

On a visual level, Buffy often took the imagery you’d expect of a show operating within the horror genre — a pretty blonde alone in a darkened alley, Dracula luring his prey with menacing charm, a demon lurking in the shadows — and twisted it into something radical and profound by making women the focal point. The emotional journey of the women involved gave Buffy’s visuals their power and visceral thrill. The show’s refusal to stick to one genre meant Buffy could be a prism for a variety of issues concerning womanhood. It pulled from melodrama, teen soaps, and even musicals to create something that hadn’t quite existed before on television. Its teen soap opera elements in its early seasons unabashedly treated even the most minor joys and tragedies of teen girlhood with the utmost importance. With its beloved season-six musical episode, “Once More With Feeling,” the series tapped into Buffy’s constant burden: having to be strong for everyone else. And using the foundation of the series, horror, Buffy turned the subtext of the transition from girlhood to womanhood into text. For Buffy, the common fear that your first love will swiftly dump you after having sex for the first time translates to him losing his soul and turning into a literal monster. Gods represent the gargantuan responsibility of grappling with adulthood and losing autonomy. Doppelgängers are the roads you never traveled, but still think about at night.

In the world of Buffy, words don’t just matter, they’re everything. The series excelled at using language as a form of empowerment and character development. Take Buffy’s dynamic with the Watcher’s Council, which oversees every new slayer. Her relationship with them was always tense at best, and this tension culminated in season three, when she makes the bold choice to no longer follow their orders. In season five, they make a surprise visit to Sunnydale to test Buffy’s skills until she decides she has had enough. This leads to one of the most triumphant and moving Buffy monologues in the series:

Power. I have it. They don’t. This bothers them. You guys didn’t come all the way from England to determine whether I was good enough to be let back in. You came to beg me to let you back. To give your jobs, your lives some semblance of meaning. You’re Watchers. Without a Slayer you’re pretty much just watching Masterpiece Theater.

This monologue, one of Buffy’s most self-assured moments, isn’t only engrossing for the obvious reason — demanding to be heard by the Watcher’s council figurehead who made so much of her teenage life hell. It also nods to one of Buffy’s greatest themes: how women negotiate power in a world that wants to keep them powerless. It proved, like so much of the series, that women could be architects of their own destiny even when the world around them tried to argue otherwise.

Conversations on the show were similarly evocative. They often played out like verbal boxing matches in which the properly placed insult or clever jab could undo the stature of even the greatest foe. Take season five’s “Fool for Love.” Buffy is off her game after being bested by a run-of-the-mill vamp, so she turns to another vampire, Spike (a deliriously fun James Marsters), to teach her how he was able to kill two Slayers. The entire episode is an amazing tête-à-tête between a more seasoned Buffy and Spike, who has shifted between enemy and reluctant ally.

“Death is your art,” Spike begins. “You make it with your hands day after day […] A part of you is desperate to know what it’s like. Where does it lead you? Now you see that’s the secret. It’s not the punch you didn’t throw or the kicks you didn’t land. Every Slayer has a death wish. Even you …”

It only takes Buffy these three words to undo Spike’s cocky bravado: “You’re beneath me,” she says, echoing a cruel remark he heard when he was human. Buffy has a lot of great moments like this. Dialogue shifts between cutting to tender and back again. Characters reveal more of themselves than they’d like in their clever quips and bitter comebacks. The dialogue of female characters like Buffy, Willow (Alyson Hannigan), and Cordelia (Charisma Carpenter) would often turn on a dime, revealing their hidden depths. Buffy was never content to present the archetypes of women you’d expect — the high-school queen bee, the bookworm, the damaged bad girl. It treasured playing with these tropes until these characters became full-fledged people.

Ask any Buffy fan about the titular character’s romantic life, and you’ll get a host of arguments about the two most important relationships she had on the series — first love Angel (a broody David Boreanaz) and archetypal bad boy Spike. The show tapped into the fertile territory of love, desire, and the growing pains that come with trying to connect, but the best decision it ever made was ending with Buffy being single. Unlike most of the shows Buffy is compared to, this series was daring enough to say that its lead heroine’s romantic journey wasn’t her most important. Adulthood for Buffy was marked not by romantic entanglements, but her relationship with her own identity and destiny.

For many, Buffy’s journey was at its strongest during her years in high school. It was when Buffy dealt with many of the touchstones of teenage-dom, heightened and filtered through horror — competition with other women, losing first loves, elders doubting her abilities. But my favorite seasons are some of the later ones, namely four through six, when she more explicitly begins her journey from girlhood to womanhood. Most teen shows don’t survive the transition to college and beyond, but Buffy was audacious enough to truly let its characters grow up and fail. The ugliness of adulthood was elegantly wrought over the course of these seasons. Season six, perhaps the show’s most divisive, sees Buffy return from the dead against her will. She’s ripped from a heavenly dimension by the friends who can’t survive without her, forcing her back to the toil of mortal life: dealing with what her mother left behind, working terrible jobs that paid little, struggling to put one foot in front of the other. You wouldn’t expect a show as fun and frothy as Buffy to get this dark, but season six became an incisive portrait of depression in the aftermath of great loss.

None of this would work without Buffy herself. That Sarah Michelle Gellar has never had a role that lived up to her skill afterward is one of pop culture’s greatest sins. Her performance — equal parts yearning and guarded, steely and open, warm and painfully human — meant that even the most outlandish moments in the series were anchored by true pathos and humanity.

As much as I love the series, its imperfections were never lost on me. Rewatching Buffy as an adult is a study in how much I’ve grown and what I expect of television today. The blinding whiteness of Buffy (which took place in Southern California, so there is no excuse) reminds me that no one who looked like me was ever truly a part of the world Buffy inhabited. I get angry when Spike tries to rape Buffy, a character choice that felt out of sync with the fabric of the series. I’m troubled that every female character on the show has an unsatisfying, often unhealthy sex life (sometimes it feels like it’s not the Hellmouth, but a sexually realized woman that is the biggest nexus of trouble). I grow annoyed every time Xander opens his mouth to shame Buffy for her choices, seemingly forgetting all the times she saved him and the world itself.

Despite all these issues, every time I hear the theme song kick in, I remember with startling clarity how deeply the show spoke to the girl I once was and still speaks to the woman I am today. Its larger cultural influence is inarguable. The show spawned a generation of leather-clad, crime-fighting virtuosos who delivered comebacks between roundhouse kicks. Yet, Buffy was never merely a Strong Female Character. She was too complex, too flawed, too human for that. There have been many well-crafted lead female characters in genre fiction to debut in the 20 years since the show’s premiere, but none as expertly acted, beautifully layered, and memorable as Buffy the Vampire Slayer.