In the “Hot Buttered Soul” era, Isaac Hayes said his gold-chain suit was a form of air-conditioning that helped him stay cool in the spotlight. Photograph by Anthony Barboza / Getty

Isaac Hayes’s legacy remains elusive. Even now, over a decade after the singer’s death, there is still no biography of him. Younger fans might remember him chiefly as the voice of Chef on “South Park,” while older ones might picture Hayes in his prime: as the voice of the hypermasculine Shaft, or the sultry Casanova who seduced fans with songs about heartache and fathered fourteen children.

But there was more to Hayes than humor and sex. Fifty years ago last summer, he released one of the most extravagantly beautiful musical manifestos of the modern era, “Hot Buttered Soul.” The forty-five-minute album, consisting of just four extended psychedelic-orchestral tracks, changed not only the sound of soul but also its scale. Hayes, by presenting himself with all the bravado of other soul men, but at half the volume, traded the big-voiced charisma that had defined soul in the nineteen-sixties for a more conceptual, introspective approach. Fittingly, the cover of “Hot Buttered Soul” featured the dome of Hayes’s shaved, bowed head.

“Isaac was just cool as shit,” said the drummer Willie Hall, who worked with Hayes at Stax Records, in Memphis. “He would look up in the top of his head, the third eye, trying to come up with an idea—boom, it would come—perfect.” Hayes is seldom remembered as an enigmatic, restless creative, and even less so as a political leader. But he was, in some ways, a race man cut from conventional cloth. He had been born into desperate poverty, and moved around to various parts of Tennessee, where his family nearly froze in the winters and starved all year long, and the experience radicalized rather than defeated him: he helped to register black voters in the South, pushed for greater black representation at Stax, and co-founded a group called the Black Knights, to protest police brutality and housing discrimination in Memphis. On “Hot Buttered Soul,” he expressed his belief in black power in more experimental terms: through ostentatious claims to musical space.

The album was both a product of and a departure from Hayes’s earlier work at Stax, where he had honed his skills as a pianist—he filled in for Booker T. Jones while Jones was away at college—and where he proved to be an especially gifted songwriter. Along with David Porter, Hayes wrote some of the label’s most iconic hits, including Sam and Dave’s “Soul Man” and “Hold On, I’m Coming.” Hayes wanted his own star turn, but, as he later explained, the Stax co-founder Jim Stewart thought his voice was “too pretty.” “At that time we were living in a James Brown era,” Hayes noted. “Rough singing . . . [but] I was a soft singer.” Sales of his 1968 solo début, “Presenting Isaac Hayes,” were unimpressive.

But then Martin Luther King, Jr., was killed, in Memphis. Hayes, who had considered King a friend, “flipped,” as he put it, and became more “rebellious” and “militant.” For a time, he also went quiet. “I could not create properly,” he said. “I was so bitter and so angry. I thought, What can I do? Well, I can’t do a thing about it, so let me become successful and powerful enough where I can have a voice to make a difference. So I . . . started writing again.” Hayes released “Hot Buttered Soul” in the summer of 1969, as part of Stax’s “Soul Explosion,” a release of twenty-seven albums designed to help the company recover from a disastrous distribution deal with Atlantic and the death of the label’s star, Otis Redding. But Hayes’s ambitions were less commercial than creative: “I didn’t give a damn if ‘Hot Buttered Soul’ didn’t sell,” he said, “because there were twenty-six other LPs to carry the load. I just wanted to do something artistic, with total freedom.”

The album contains no rage or protest in the conventional sense. Hayes mentions race only once, in a mystifying lyric on the track “Hyperbolicsyllabicsesquedalymistic”: “A slave’s on a horse every time she explores / Just heard a discussion about, uh, racial relations.” But the album’s very largesse was political: Hayes had internalized King’s death, one of the era’s preëminent signs of black vulnerability, and reëmerged as a giant.

Three quick drumbeats and the album opens, operatically, with the string arrangement of “Walk On By”: a velvet curtain pulled back to reveal a production that combines the opulence of chamber music with that of funk. The mounting orchestra is intercut with Harold Beane’s fuzz-heavy guitar. While the song, composed by Burt Bacharach, had been a 1964 crossover hit for Dionne Warwick, Hayes wanted his cover, he said, to target “the black listening audience.” That focus comes through in his ad-libs: he doesn’t just accuse his lover of “saying goodbye”; instead, he tells her, “You put the hurt on me! You socked it to me!” There is a delicious irony in Hayes’s decision to remake a song about wanting to go unnoticed into an epic tour de force. Don’t mind me, the lyrics say; I am inescapable, the music says.

“Hyperbolicsyllabicsesquedalymistic,” while it takes the concept of going big to an imaginative extreme, is another serious exercise in the refusal of fear and containment. Listen closely to Marvell Thomas’s piano solo, and you can hear the shaking of chains. When Hayes covers Jimmy Webb’s “By the Time I Get to Phoenix,” which had been a hit for the country singer Glen Campbell, he prefaces the song with a nearly nine-minute monologue about a man who leaves his wife after he catches her cheating on him eight times. The monologue not only epitomizes Hayes’s insistence on taking his time, it also changes the song’s narrative by making the man’s departure a response to continued betrayal. The theme of infidelity shapes Hayes’s cover of “One Woman,” as well: “One woman’s making my home / while the other woman’s making me do wrong.” To situate the album in the wake of King’s death is to hear its obsession with betrayal as not only personal but also social—as suggestive of the ways that black people have been consistently betrayed by the state and yet still rise, refuse, preen.

Hayes’s sartorial experiments were the visual counterparts to his sonic largesse. Whereas the cover of his début album pictured the singer in a top hat and a tuxedo, with “Hot Buttered Soul,” Hayes exchanged old-fashioned masculine glamour for flamboyant camp. The Jet writer Chester Higgins compared him to a “strutting, virile peacock” onstage, with luscious furs, colored tights, and his trend-setting bald head. Hayes’s most iconic outfit in this era was a gold-chained “suit,” which he variously described in pragmatic, political, and sexual terms—calling it a form of air-conditioning that helped him stay cool in the spotlight, as well as a symbol of the end of black bondage and “a sex thing.”

The meaning of Hayes’s music was similarly complex. But his seizure of musical space—literalized in the LP jacket for “Black Moses,” which unfolded to reveal a full-length portrait of Hayes in a robe, his arms outstretched—made a political statement at a time when black people were being made to feel acutely unwelcome in the public sphere: patrolled by police in their own neighborhoods, maimed and killed for being “in the wrong place at the wrong time.” Hayes took up time and space as if it were owed him, and listeners responded. “Hot Buttered Soul,” despite being what the critic Phyl Garland called “probably the strangest record hit of the year,” became the first Stax LP to go gold. It sold a million records to black consumers alone.

How exactly Hayes emerged from poverty and trauma to fashion himself so deeply at home in the world is one of the miracles of soul music. But, if the source of his confidence is mysterious, its destination is clear: Hayes’s audacious claims to space and selfhood are everywhere in hip-hop. Countless tracks, perhaps most notably Wu-Tang Clan’s “I Can’t Go to Sleep,” sample “Walk On By.” We also see Hayes’s legacy in hip-hop fashion trends that explode and exploit America’s rags-to-riches mythos. We can even hear Hayes in the quieter aesthetic of conceptual artists like Solange and Sampha. These singers seem to have internalized one of Hayes’s key lessons, which was on display when, in the summer of 1972, he headlined the Wattstax Festival, in Los Angeles. What the scene of the velvet-voiced Hayes playing there, before a hundred thousand black fans, meant was that you don’t have to raise your voice to call an army. Sometimes you just have to stretch out your arms.