On June 8, 1974, Dolly Parton's "I Will Always Love You" started its first and only week at No. 1 on the charts. It was the second chart-topper from her Jolene album — the title track also spent a week at No. 1 earlier in the year — and was certified gold in 2017.

The lyrics of "I Will Always Love You" assert a woman's need to move forward, while still expressing gratitude for her past. They're based on a true story, Parton told the Tennessean in 2015: She wanted to explain her decision to leave The Porter Wagoner Show and strike out on her own.

"'How am I gonna make [Wagoner] understand how much I appreciate everything, but that I have to go?'" Parton says she thought to herself. "So I went home and I thought, 'Well, what do you do best? You write songs.' So I sat down and I wrote this song."

Appropriately, Parton's voice is squarely at the forefront of the mix. While occasionally there's a slight tremble to her tone, her delivery overall is strong and forthright as she speaks her truth. At first, Parton is overly deferential while asserting her reasons for leaving ("If I should stay / I would only be in your way"), although her tender confidence soon wins out: "So I'll go, but I know / I'll think of you each step of the way." In fact, as the song progresses, it's clear that she has leverage in this situation: "Goodbye, please don't cry / We both know that I'm not what you need."

The emotional apex of "I Will Always Love You" uses unadorned and economical language ("I hope life treats you kind / And I hope that you have all / That you ever dreamed of") to express parting thanks. Other songwriters might be inclined to overdo the sentiment at this point; however, the straightforward, raw emotion of the song's lyrics underscores Parton's strength as a songwriter. "I Will Always Love You" might have been written about a specific incident, but the feelings she expresses are wholly universal.

"I Will Always Love You" endures because it's so intertwined with Parton and her own legacy.

They're also timeless, a fact that's underscored by the song's steady pop culture presence through the decades. "I Will Always Love You" has been covered by multiple artists, including Linda Ronstadt, LeAnn Rimes and Lulu Roman. Parton herself also took a re-cut version of the song (from the soundtrack of The Best Little Whorehouse in Texas) to No. 1 in 1982, and re-recorded "I Will Always Love You" with Vince Gill in 1995, for his greatest hits album Souvenirs. Their duet version peaked at No. 15 on the Billboard charts, and the pair also sang it at the 1995 CMA Awards.

Of course, the song joined music's upper echelon thanks to Whitney Houston's blockbuster version from 1992's The Bodyguard. Thanks to a powerful vocal performance, the late pop icon amplified the range of emotions contained within the song — happiness, regret, sadness, nostalgia — and transformed the song into an unstoppable soul / R&B anthem. Houston's version topped the pop charts for an impressive 14 weeks, and introduced the song to an entirely new generation of music fans.

"One day I was riding along in the car and had just turned the radio on, and I heard her start that a cappella, like, 'If I should stay,'" Parton recalled to CNN in 2003. "And it took me like a few seconds, and I thought, 'What is that? That's so familiar.' And then when she went into, you know, like the 'I will always love you,' I just about had a heart attack and died. I just about wrecked. It was a great feeling, though. What a great record she did on that."

Houston's version also illustrates one reason the song endures: malleability. "I Will Always Love You" resembles a standard, in that while its basic chords and structure are in place, the song's arrangements and instrumentation leave room for broad interpretations. Parton's original is sparse, and driven by mournful banjo, pedal steel and guitar, as well as whispers of piano and fiddle, before a chorus of background harmonies appear near the end, like a ghostly church choir. Houston's take is also spare at first, although its production is modern and sparkling — and when she goes for the high note at the end, her stunning octave-jump is pure cathartic anguish.

However, the forgiveness built into "I Will Always Love You" also cements the song's longevity. Parton could've easily gone with bitterness or anger as a parting lyrical shot toward Wagoner. However, her simple wish — "And I wish you joy and happiness / But above all this, I wish you love" — embodies the kind of gentle grace to which we all aspire when facing a tough goodbye.

Dolly Parton I Will Always Love You single cover

That gesture certainly wasn't lost on Wagoner in 2007, when Parton sang the song for him during a Grand Ole Opry special. The one-time partners weren't on great terms after Parton left, although their awkwardness had dissipated by the time this particular night rolled around.

"It was the most emotional night that I've ever spent at the Opry in my whole life," Wagoner told Yahoo! Music. "And Dolly, of course, sang that song, "I Will Always Love You," and they had me sitting on a stool, and she just came out and wiped some of the tears away ... She meant it for me and wrote it for me, she said. That's a wonderful thing that she stood there and sang it for the whole world to see. And the evening was unbelievable."

As that gesture implies, "I Will Always Love You" also endures because it's so intertwined with Parton and her own legacy. She's fiercely protective of the song, and shepherds it with great care and delicacy. In fact, when Elvis Presley wanted to cut "I Will Always Love You," Parton declined after Col. Tom Parker wanted her to sign over half of her rights to Presley.

“I said, 'I’m really sorry,' and I cried all night," Parton told CMT. "I mean, it was like the worst thing. You know, it’s like, 'Oh, my God … Elvis Presley.' And other people were saying, 'You’re nuts. It’s Elvis Presley. I mean, hell, I’d give him all of it.' I said, 'I can’t do that. Something in my heart says, 'Don’t do that.' And I just didn’t do it, and they just didn’t do it.

"But I always wondered what it would sound like. I know he’d kill it. Don’t you? He would have killed it. But anyway, so he didn’t," she added. "Then when Whitney [Houston’s version] came out, I made enough money to buy Graceland."

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