The last time Jeff Mangum toured behind the songs he wrote for Neutral Milk Hotel, the world was a very different place. One difference in particular is that in late 1998, when the band hit Chicago on the only real tour it ever did to promote its landmark album, In the Aeroplane Over the Sea, it was booked at tiny Lincoln Park club Lounge Ax. When Mangum rolled through early last week as a solo act, he played two nights at the 1,000-seat Athenaeum Theatre, both of which sold out in minutes—online scalpers were selling tickets for almost $200 in the days just before the shows.

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Clearly the 13 or so intervening years have been very good to Mangum, despite the fact that he disbanded NMH shortly after that 1998 tour and has spent most of his time since then out of the music business and stubbornly invisible to the public eye. Since Aeroplane his discography is extremely slim. He’s contributed to Major Organ and the Adding Machine, an odd album of sound collages by former bandmates and other members of Elephant 6 (a loose collective Mangum cofounded in the late 80s), attempted to undercut bootleggers with a live solo album, and compiled a collection of field recordings called Orange Twin Field Works: Volume 1 from a folk festival in Bulgaria, but he’s released only one new original song—and that was as a widget embedded in his website. For a while he would occasionally show up onstage with Elephant 6-­associated acts, but until very recently he wasn’t playing proper shows. His existence has been so hermitlike that when you type “Jeff Mangum” into Google it suggests adding the word “crazy” or “dead” to your search.

This quasi-religious fervor—call it the Jeff Mangum Effect—only intensified once the man himself took the stage, unaccompanied, and sat in a chair surrounded by acoustic guitars. After the deafening applause that greeted his appearance had died down, he started into Aeroplane‘s “Two Headed Boy Pt. 2,” and from where I sat the crowd was an unbroken sea of rapt faces. A lot of people were singing along—a practice Mangum encourages—but absolutely none of them were talking to one another or checking their phones. I can’t remember the last time I saw that at a show.