Ten years ago this month, a songwriter from nowhere and his ramshackle band brought out one of the few truly great albums of this generation, a musical curio so gloriously odd that it almost defies explanation. The group called itself Neutral Milk Hotel, and the record, In the Aeroplane Over the Sea, is a concept album about Anne Frank in which vocals about lost Siamese twins and semen-stained mountaintops mingle with the sounds of musical saws, fuzzy tape loops, and an amateur psychedelic brass band. It seems like a formula that would blister your eardrums, yet Aeroplane is a gorgeous, much adored work of art. In 2003, the alternative music magazine Magnet dubbed it the best album of the past decade—better than Nirvana, better than Radiohead.

While the record sells better today than ever, you won’t see Neutral Milk Hotel onstage anytime soon because, for all intents and purposes, they’ve vanished into thin air. At the end of Aeroplane’s final song, you can hear Jeff Mangum—the band’s singer, songwriter, and all-around mastermind—set down his guitar and walk off, and, minus a few months of under-the-radar touring, that’s exactly what Mangum did in real life. When the major labels and the glossy magazines and the half-crazed fans came calling, Mangum never responded. There was no breakup announcement, no reason given for the radio silence—he just faded out. After a decade of speculation, sightings, and hoaxes, his story remains a mystery: Why did he decide to disappear? And where has Mangum gone?

Even before his public vanishing act, Mangum was something of an elusive character. Raised in the arts vortex of Ruston, La., he bristled at his hometown’s jocks-and-booze ethic and hoped from an early age to unchain his creative spirit. In the early ‘90s, Mangum and a few friends formed a now-legendary collective called Elephant Six, which grew to encompass dozens of strangely named bands creating eclectic music mostly for their own enjoyment. Yet Mangum himself seldom stayed in one place for long; he constantly hopped from city to city, acoustic guitar in hand. At home in the collective’s base of Athens, Ga., or out on his peregrinations, Mangum cut a strange figure: a long-locked, intense-looking man with a gale-strength singing voice who liked to wear garish thrift-store sweaters and embellish the cuffs of his pants with cartoon sketchings.

Because he suffered from night terrors, Mangum often stayed up until dawn working on his songs, sometimes addressing them to the ghosts in a haunted closet. At first, this method produced modest results: His first album, On Avery Island (1996), showed flashes of promise but had its sludgy and spotty patches. One day, Mangum wandered into a bookstore and happened upon a copy of Anne Frank’s The Diary of a Young Girl. The book consumed him. After finishing it, he spent a few days crying over Frank’s story. As he told a Puncture magazine interviewer before Aeroplane’s release, “I would go to bed every night and have dreams about having a time machine and somehow I’d have the ability to move through time and space freely, and save Anne Frank. Do you think that’s embarrassing?” The songs and lyrics he started writing about Frank could be so nightmarish in vision that Mangum grew afraid of what was issuing from his brain: verses about “pianos filled with flames” and eating “tomatoes and radio wires.” At times, he seems possessed, singing on Aeroplane’s title track, “Anna’s ghost all around/ Hear her voice as it’s rolling and ringing through me.”

In the Aeroplane Over the Sea is so expansive in its weirdness that one of its 11 songs is a rollicking bagpipe jam—yet it would be wrong to call it a “cult” record, since that would imply it’s some sort of flawed art-school project. Sure, Aeroplane occasionally sounds like a mariachi circus fed through a broken amplifier, but it all weaves together as Mangum guides the proceedings with percussive guitar strumming, singalong melodies, and his booming, emotive voice. The album plays like a document from a parallel-universe version of the 1940s, inlaid with Mangum’s haunting lyrics: “And here’s where your mother sleeps/ And here is the room where your brothers were born/ Indentions in the sheets/ Where their bodies once moved but don’t move anymore.” Aeroplane isn’t about airtight instrumentation or tricky songwriting—most of the songs have just three or four chords—but about a remarkable range of feeling put into melody. (Mangum recorded his part of the song “Oh Comely” in one scratch take, at the end of which you can hear a stunned band member yell “Holy shit!” in the background.)

When Aeroplane first debuted, sales took a while to warm up. Those who found the record would appear at shows and (to the annoyance of many audience members) collectively drown out Mangum’s singing with their own rendition, but this was still indie music’s dark, pre-blog era. By the time magazines started paying attention, toward the end of 1998, Mangum already had one foot out the door. Worn down by months of touring, he grew fed up with discussing himself and explaining his lyrics, eventually declining to accept any calls—yet friends say he still fixated on every word written about him. As his bandmates pressed him to capitalize on Neutral Milk Hotel’s success, he withdrew more and more. When R.E.M. offered a chance to open for them, he said no. And for the last decade, that’s nearly all he’s said.

As Aeroplane’s legend began to build, Mangum kept himself busy by having a total nervous breakdown. Laura Carter, his then-girlfriend, told the Atlanta alt-weekly Creative Loafing that he spent entire days sitting in his house in a state of near panic, wearing a pair of old slippers and doing absolutely nothing. He became paranoid, hoarding rice for the inevitable post-Y2K apocalypse. Since 1998, Mangum has rejected every interview request save one 2002 conversation with Pitchfork in which he explained his meltdown. “I went through a period, after Aeroplane, when a lot of the basic assumptions I held about reality started crumbling,” he said. One of those assumptions was that music would somehow erase his problems. “I guess I had this idea that if we all created our dream we could live happily ever after,” he continued. “So when so many of our dreams had come true and yet I still saw that so many of my friends were in a lot of pain … I saw their pain from a different perspective and realized that I can’t just sing my way out of all this suffering.”

It took Mangum years to rebuild himself after this spiritual crisis—and since part of that crisis was his recognition that music would never save him from his demons, he couldn’t very well embark on another record. So he wandered the globe to find spiritual balance, even spending time in a monastery. (Aeroplane’s steady sales helped finance the quest; the album still moves a reported 25,000 copies a year.) Occasionally, Mangum flitted ever so briefly into the public eye. He released a disc of field recordings of Bulgarian folk music, then disappeared. Calling himself “Jefferson,” he hosted a late-night radio show on New Jersey’s WFMU a few times until he was discovered, then vanished once again. Sometimes he’ll appear onstage at friends’ rock shows for a song, sending the crowd into paroxysms—but when those friends suggest he record his own music, they say he becomes evasive.

Mangum’s continued silence has angered some fans, who accuse him of being selfish or “indifferent to his talent,” as if musical ability comes with some sort of obligation to society. At least once a year, someone writes a hoax message from Mangum and posts it online—generally throwing in some fanciful verbal junk to bilk fans into believing it’s the genius himself wielding the keyboard. Some have announced forthcoming records or tours, while others have revealed the long-hidden sources of Mangum’s misanthropy; they’ve all been debunked. All we really know for sure is this: According to his record label, Mangum now lives in New York City. He recently married filmmaker Astra Taylor. Friends say he still creates art and that he seems “very happy.” If he has plans to record more music, he hasn’t told anyone.

And if Aeroplane really is Jeff Mangum’s final statement to the universe, maybe we should be happy with that—not because of some tired line about going out at your peak (which he likely didn’t reach), but because his story is a kind of modern fable. Many fans see his disappearance only in selfish terms: They’ve been deprived of more great music for no good reason. They can’t understand why Mangum would shun success just to shuffle through his days, and, indeed, when musicians abandon this much promise, the culprit is usually drugs or debilitating accidents or people named Yoko. So he must have gone nuts, right? Well, no. After all, what if Mangum is just being honest? What if he poured his life into achieving musical success only to discover that it wasn’t going to make him happy, so he elected to make a clean break and move on? We should all be so crazy.

As always, though, hope for Mangum’s return still glimmers. Last month brought news that he may play a guy in a lobster suit in a soon-to-be-released conceptual film. But who knows? You can’t see inside the suit.