In April, 1971, Rolling Stone reviewed the début album by a band with a name better suited to a law firm: Emerson, Lake & Palmer. The reviewer liked what he heard, although he couldn’t quite define it. “I suppose that your local newspaper might call it ‘jazz-influenced classical-rock,’ ” he wrote. In fact, a term was being adopted for this hybrid of highbrow and lowbrow. People called it progressive rock, or prog rock: a genre intent on proving that rock and roll didn’t have to be simple and silly—it could be complicated and silly instead. In the early nineteen-seventies, E.L.P., alongside several more or less like-minded British groups—King Crimson, Yes, and Genesis, as well as Jethro Tull and Pink Floyd—went, in the space of a few years, from curiosities to rock stars.