When Dolly Parton wrote and recorded "I Will Always Love You" in 1973, it was to acknowledge her sadness at leaving behind her musical and TV partner Porter Wagoner. Emphasizing her bond with her mentor, Parton sings the “I” and “you” of the title’s chorus in the same demure way, and does so on the same modest note; the result is an understated, miniature marvel.

When Kevin Costner teamed with Whitney Houston for their 1992 blockbuster The Bodyguard, he originally wanted his costar to cover Jimmy Ruffin’s 1966 Motown classic What Becomes of the Brokenhearted," but UK pop singer Paul Young had just hit the charts with his rendition for Fried Green Tomatoes. Costner then suggested “I Will Always Love You,” and reportedly brought Houston Linda Ronstadt’s 1975 version, which replaces Parton’s spoken third verse with piano and slide guitar solos, and features a far bigger, string-laden arrangement. Producer David Foster contends that he studied “all the various versions that had been recorded,” which no doubt included Parton’s 1982 update for The Little Best Whorehouse in Texas, a remake that enabled the star to top the country charts a second time with her career-changing song. Suddenly Foster understood how to shape it for Houston.

Like Queen’s “Bohemian Rhapsody” but unlike nearly all other pop hits, the Houston version begins a cappella. The echo effects are extreme, but tasteful, as if we’re seeing her near-naked body cloaked in a sheer negligee. Houston takes liberties with tempo, holding notes and pausing without an orchestra in tow. Instruments suddenly appear and get louder–not like they’re played that way, but as if the guy at the mixing deck simply moved up the backing tracks’ sliders. An electronic keyboard suggests a church organ, and a couple of additional measures appear between the first chorus and the second verse; this extra “You, my darling, you, mmm-mmm-mmm” helps to make a country song ooze like jazz.

The echo intensifies further, both on Houston’s voice and on a drumstick clacking against a snare rim. The Ronstadt version’s piano and steel guitar solos get replaced by wailing ‘80s-style sax, then Houston sings the Parton-spoken third verse. Her vocal style here is decidedly more gospel and determined: Where Parton hits the notes and then backs off, Houston belts. “I wish you JOY and happiness,” she declares. A fleeting E major chord anticipates change, but first there’s a major pause. Then BOOM go the cavernous drums and UP goes the key from a tentative A major to a triumphant B major–a drums-and-key-change combo perfected on countless hits by Houston’s label mate Barry Manilow. It’s the musical equivalent of Houston getting on the airplane at the end of The Bodyguard; suddenly shouting “Wait!” to the pilot, and then dashing across the runway into Costner’s protective, wounded arms.

Here the singer swings into superstar mode: Houston attacks the “I”s of the chorus, then releases her “you”s with a flurry of melisma and long-held notes that shout me, Me, ME! Now the subject and object of the song’s title no longer link in a succinct, humble package. Rather than a heartbroken vision of two equals linked through everlasting love, the one-third longer and considerably louder Foster/Houston adaptation emphasizes physical stamina and emotional resilience.

These musical and sentimental shifts make this “I Will Always Love You” one of pop’s most challenging ballads; the A to negligible E to B major key change is next to impossible; the same goes for the way Houston belts from the chest, momentarily flips into head tones for the high notes, and back to the chest. If those challenges don’t trip up the fool-hearted American Idol contestant, attempting to approximate Houston’s mix of devotion and power surely will.

These changes also helped make possible the song’s astronomical success. Nothing succeeds like confidence, and Houston’s version positively exudes it, with results that transcended language and geographical divisions. In the US, the song remained at Number One for 14 weeks from the end of November 1992 to the beginning of March 1993–the end of America’s first George Bush era and the beginning of the Bill Clinton years. An adult pop and soul alternative to that period’s boyish grunge and gansta rap, the disc from which it came was even bigger: The Bodyguard soundtrack reigned over the Billboard 200 for 20 nonconsecutive weeks, has sold over 17 million copies in America, and at an estimated 44 million copies worldwide is ranked the fourth best-selling album of all time. For a seemingly interminable stretch, “I Will Always Love You” was nearly impossible to escape; its combined intensity and media saturation made the track one of the ‘90s most beloved and loathed hits.

This cultural dominance didn’t come from nowhere. Even during Beatlemania’s height, movie soundtracks like My Fair Lady and The Sound of Music regularly trumped all but the biggest rock. The Bodyguard is a drama, not a musical, in which music both intertwines with plot and underscores its emotional currents like Saturday Night Fever did with record-establishing success in the '70s. At an estimated worldwide 10 million copies, the top-selling song of 1991 and another one of the biggest singles of all time, Bryan Adams’ “(Everything I Do) I Do It for You” from Robin Hood: Prince of Thieves set a power ballad precedent that Houston’s biggest hit exceeded. Not until 1997 with Elton John’s Princess Diana-dedicated rerecording of “Candle in the Wind” and Céline Dion’s “My Heart Will Go On”–a Titanic ballad structured much like “I Will Always Love You” with a remarkably similar message–was Houston’s sales record broken.

The Bodyguard isn’t a great or revolutionary movie: Houston essentially plays herself as an ambitious pop star, and white hunk Costner acts as her protector. But it is a box office smash in which interracial romance is front and center but never once an issue, and that’s a rare and beautiful thing. In Houston’s own career, race was often a major if unspoken concern; in order to compete with the rock bands, pop icons, and rappers of her day, Houston had to be prettier, sing louder, be less threatening, and outsell everyone. She was arguably the first soul diva to become a commodity from the very start, a role that must’ve been unfathomably challenging for the extraordinarily gifted daughter of Cissy Houston–a background singer for Aretha Franklin–and niece of Dionne Warwick.

I interviewed Whitney Houston exactly 12 years ago. She was about to release her 2000 Greatest Hits package, and just hours away from performing at Clive Davis’s annual pre-Grammy party; the same event she was preparing for on the afternoon of her death. It was a surreal couple of hours: Destiny’s Child dropped by in full costume; Bobby Brown playfully sparred with his wife when she commanded him to get her some miso soup, “like now.” Houston was both disarmingly frank and intimidatingly petulant; it was a challenge just to keep up, but worth it. Her sexuality was then her most controversial subject. By the time the interview hit the stands and for the next 12 years, the permanent subject on everyone’s lips was her drug intake.

“Sometimes, I swear to you, it feels like nothing is going my way,” Houston remarked as we concluded. “Then I look at my little girl and know that she needs me for me and not anything else. That makes me wanna live on so much harder, ’cause I can’t stand to think the world would teach her something I wouldn’t teach her. That makes me live, baby.”