In a 2003 interview with CMJ New Music Monthly, Aesop Rock does his best to dismantle his mythology. The piece paints a portrait of a hyperactive mind wracked with executive dysfunction, the plight of an artist caught between the gears of his own brain. Standing in his messy apartment, replete with spent matchbooks and ashtrays overflowing onto the floor, Aes looks on as El-P, his labelmate, and Teal, his publicist, pick up empty water bottles and discarded CDRs.

It’s easy to imagine him spinning in circles, ambivalent about the profile and unsure of how to help his friends clean; his quotes oscillate between a slight grandiloquence about his records being classics and a rattling anxiety about how he’s perceived. This was during the press cycle for Bazooka Tooth, his nervy fourth record and follow-up-slash-fuck-you to 2001’s Labor Days, the breakthrough that propelled him into minor rap stardom. People were calling him a “genius,” but, as he tells the reporter, “Look at my fucking crib. There’s Pepto Bismol spilled on the freaking coffee table.”

That feeling had been bubbling up in Aes since he’d started getting press. Music journalists treated him as a specimen to dissect, while posters on Al Gore’s internet viewed him as the greatest lyricist to touch a mic. He didn’t see himself as either. The reality was more straightforward, humanizing even: Born Ian Mathias Bavitz, in 1976, between brothers Graham and Chris, he was raised in a quiet part of Suffolk County, New York. He spent most of his free time drawing, a passion that would lead him to Boston University, where he graduated in 1998 with a Certificate of Fine Arts. Although he loved Run-DMC and the Beastie Boys, there were no grand designs to grow up and become a rapper. In interviews, he shrugged off any connection between his visual art practice and his music career, and when asked about his dense, cluttered lyrics, he’d respond, “I just write about what I see and perform it with conviction. It’s mad obvious when cats act deeper than they really are, so it doesn’t make sense to do that.”

But in the late ’90s and early ’00s, as Aes built a buzz in the New York rap underground, fans and critics began regarding him as a mythical figure sent to Earth to redefine hip-hop—to transcend it altogether. He bristled at what he perceived to be a disingenuous read of his work, a push to label him as anything other than a rapper simply making rap music. “All these subgenres are things that didn’t exist when I first started rapping,” he says in that same CMJ interview. “Now it’s like ‘leader of the nation of avant-hop prog-rap’—I don’t even know what the fuck that means!”.

Aes cut an unconventional figure for a rapper, a tall, lanky white guy with dinner plate eyeballs, a perpetually unkempt beard, and an air of hypervigilance. In video footage from that era, he looks constantly on edge, staring into the middle distance and pulling another cigarette from the quickly diminishing pack. The voice that emerged from that wiry frame was immediately striking: a gravelly baritone, frayed by smoke and tar, vowels hammered on the anvil of a thick Long Island accent. He rapped in overstuffed sentences through a maze of 50-cent words and ornate imagery. Each lyric felt like a proclamation from some smirking deity hiding the meaning of life in a cryptogram, something he’d cop to on 2002’s “Nickel Plated Pockets”: “If this means anything at all anyway, it’s a riddle.” He could encapsulate the vastness of existential churning in only a few bars, like this passage from “The Tugboat Complex,” an early-career loosie that appeared on Inside Out Vol. 1: A Fool Blown Compilation:

I slide like Kodachrome, wrote a poem for every planet
Type their mileage from the sun on an envelope, licked it, stamped it
Got eight thank-yous in the mail, but nine planets means there’s one left
Only the Earth would thank me later with a breathtaking sunset

Aes’ style wasn’t without precedent. During the Clinton years, as hip-hop entered its second decade, rappers began to push at its boundaries, developing new rhythmic pockets, embracing the slipperiness of language, and delving into topics previously untouched. MCs like Nas and Big L gleefully discovered how many rhyming syllables they could stack together; Aceyalone waxed philosophical about concepts like the passage of time and laws of human attraction; Camp Lo created entire dialects out of slang terms both familiar and fabricated; Company Flow filtered sci-fi, dystopic paranoia through classic rap braggadocio. Blockhead, Aes’s best friend and frequent collaborator, once said that when they first met, Aes resembled Saafir, the late Oakland rapper whose hypnotic 1994 debut, Boxcar Sessions, had the density of a neutron star, a tangle of triple entendres and obscure reference points. In 2000, the same year Aes released Float, Ghostface Killah rewrote the English language with his absurdist, mafioso masterpiece, Supreme Clientele.

Small labels like Fondle ’Em, Rawkus, and Rhymesayers dominated the underground, constantly releasing ambitious, forward-thinking records. Their fanbase was often labeled “backpackers,” a somewhat derogatory term for rap nerds who championed graffiti writers and “conscious” MCs (rappers like Common or Talib Kweli who combined secular spirituality with social justice), traded bits of Scribble Jam lore, dissected lyrics on web forums, and shied away from the sleek, jiggy sounds on Top 40 countdowns. The etymology of “backpacker” is a little murky; some believe it references graffiti writers who’d turn up at rap shows with backpacks full of spray cans, while others say it refers to young fans who’d carry around records of their favorite niche artists. Regardless of its origins, backpack rap emerged as a subgenre for those seeking topics beyond street tales or shopping sprees. It could be corny, embracing a cringey “lyrical miracle” vibe, or cerebral and strange. Eventually, it lost the negative connotations and simply became a synonym for “alternative.”

Later in the decade, the underground splintered further, as even smaller labels like anticon. and Peanuts & Corn became bastions of experimentalism, issuing albums of brooding, almost ambient instrumentals and nearly inscrutable lyrics. It was a time of fervent research and development, tearing hip-hop to the studs, studying its blueprints, and attempting to build something new. As Cash Money took over for the ’99 and the 2000, and Jay-Z smoked cigars on yachts filled with video vixens, some rap fans dismissed anything on the radio and music channels as formulaic or cheap.

There was an endless, circular debate on message boards about what constituted “real hip-hop,” and many argued that emphasis on writing over everything—multi-syllabic rhymes, complicated concepts, clever punchlines—was the only mark of worthwhile music. So-called “abstract rap” offered solace to those who felt alienated by the mainstream, and, in hindsight, lacked the critical understanding that hip-hop had always been experimental at its core. When Aesop Rock dropped Float, he was greeted like the perfect avatar of that concentrated zeitgeist, the culmination of the decade’s fence testing: Here was an MC clearly raised on the “yes yes y’all” era, playing with language like a cat teasing its prey, discovering innovative cadences, and rapping like his cortisol levels spiked with every sunrise.

Remarkably, Float seemed less like a refinement of his previous works and more like a product of a confident artist in perpetual motion. Music for Earthworms, a 1998 compilation of tracks Aes recorded with producer Dub-L, was a modest cult hit, selling 200 hand-assembled copies before the toll of xeroxing and cutting each cover became too much. Compared with Float—or most of Aes’ discography for that matter—songs like “Abandon All Hope,” a creeping mid-tempo jam casting his boasts as carvings on Hell’s door, or “The Substance,” a syrupy meditation on the cold indifference of the universe, wouldn’t seem out of place. 1999’s Appleseed, which sold 10 times as many copies, is just that much more polished, shedding the four-track murk to be more present and assured.

Around that time, Doseone, the cLOUDDEAD member who guested on Appleseed’s final track, “Odessa,” had become an A&R for Mush, a small Cincinnati studio-turned-label that had put out a number of cLOUDDEAD 10-inches. In 1999, Dose approached Aes and brokered a one-album deal, the details of which were outlined in a simple three-page contract. Aes had always been skeptical of labels; why sign anything that would probably never pay the bills and ultimately complicate the fun of making music? But, given the homespun success of his first two projects, the chance to have someone else cover the cost of full-color artwork was persuasive. “I had about 20 songs,” he said in a 2007 interview with Caught in the Crossfire. “I thought, ‘Yeah, let’s just put them all on there,’ and that was the first official record.”

There’s a ramshackle, lo-fi charm to Float that feels immediate, as if each new thought that crossed through Aes’ mind instantly breaks containment. He and Blockhead, who produced about half the record (Aes himself provided the other half), recorded the album on a Roland VS-880 digital workstation, a budget-friendly studio-in-a-box that’s nonetheless a slight step up from a cassette four-track. Both Aes and Blockhead (and Omega One, who contributed the beat for “Skip Town”) composed on ASR-10 samplers but didn’t separate the stems of their beats, bouncing everything as a stereo mix. Aes tracked his vocals without a stand, gripping a Shure SM-58, the stalwart, affordable mic found at every live venue, in his fist. There’s a tinny resonance coating Aes’ rich voice, and plosives abound, suggesting loose, shambling sessions shot through with a frantic, wide-eyed energy.

It’s an overwhelming album. Aes fills nearly every space with words, emphasizing specific lines with infinite layers of his voice and ad-libs zipping around in the background like agitated bees. There’s almost no breathing room, save for Blockhead’s three instrumental interludes, but even those—especially “Dinner With Blockhead,” a somersaulting bandoneon loop perforated by tear-the-club-up drums—are packed to the gills.

Float lives all over the map but never feels like it’s overreaching or clashing with itself. Consider how well the rain-streaked Gershwin jazz of “No Splash,” or the Hitchcock score strings of “Oxygen,” or the ’80s noir electro of “Fascination” hang together, mesmerizing yet transportive. Each cut is filled with ear candy, like the internal rhymes Aes flexes on “Spare a Match” (“Spare a match for the most distorted orchid in the patch/Assorted orphans coursed in morbid orbit forward toward the traps”), or the rhythmic tension between the guitar sample and dragging drums in “The Mayor and the Crook.” “Big Bang” is especially emblematic of Float’s restless sense of discovery: Aes hits a double-time flow during the hook, something few East Coast rappers were attempting in the late ’90s. When it slows to a half-time lurch for the third verse, it sheds the baroque cello and violin loops and gains synth arpeggiations typical of the Mannie Fresh and Beats by the Pound singles that dominated the airwaves.

Aes raps as though he’s running out of time, desperate to convey his message before being carried off by death or angels or some other unknown force. There’s an air of paranoia hanging over the record, manifested most clearly in the chorus of “Commencement at the Obedience Academy”: “Must not sleep, must warn others,” a phrase so deeply held that he tattooed it on his arms. His words careen around each other; you get the sense he’s constantly trying to hold himself together like a dropped pie. Verses move from acidic to nakedly emotional within the space of a few bars. “My tummy’s full of glass because I promised my friend I’d chew up the bottle if he truly drank the poison,” he says on “The Mayor and the Crook,” only to follow it up later with “I cherish the Ferris wheel’s revolutions not because the ride enthralls/But more simply to the fact that it still revolves.”

At the beginning of “How to Be a Carpenter,” a song about exploring one’s artistic practice, Aes offers a parable:

I used to have a rope ladder, but tattered were the rungs
I strung it from the highest willow, trying to hug the sun
The seventh level buckled, and I tumbled from the summit
Now I’m back to re-climb, and this time light my cigarette from it

It’s a striking image, one of the most memorable quotes from an album flush with quotables. As his work progressed, he’d go on to recreate that approach, crafting stories within stories, little four- to six-bar asides that deepen whatever concept he’s working in. If taken out of the context of his lengthy, storied discography, Float stands as a masterful statement, unwavering and aware of its vision. But trace its lines, and you’ll recognize it as the road map for everything he’d go on to do. “6B Panorama,” in which Aes looks out at Avenue A and 11th Street, in the East Village, and describes the vibrant world, presages the hyper-detailed observations in songs like “Bird School” or “Fumes.” On “Big Bang,” he “smells the warm blood of the bill collector knocking,” a theme he’d immediately revisit on 2001’s Labor Days. Float is the load-bearing piece of Aesop Rock’s catalog, a complete work and an endless wellspring for one of rap’s strangest and most acclaimed careers.