Performing was always a magical, transformative experience for Gregg Allman. “I’ve walked onstage with an abscessed tooth and as soon as you get out there, it goes away. Walk offstage, it comes back.

Thanks to a distinct melting pot of genres, a scintillating dual guitar act that reinvented the wheel for two-pronged player partnerships and a borderline unrivaled live energy, the Allman Brothers ...