Call them depraved, call them unsettling, call them pioneers in the way they incited near riotous responses with their live freak show, but if they are any one thing, the Butthole Surfers are unforgettable. With their volatile performance art and noisy, at times hardcore, at times avant-garde sound, the Butthole Surfers permeated the American underground with a wicked sense of humor and experimental approach to writing, recording, and performing. This photograph, captured by rock photographer Clayton Call, shows the band backstage at a 1991 concert at San Francisco's Warfield Theatre, a year before they entered the mainstream via a label deal with Capitol Records and studio time with, yup, Led Zeppelin's John Paul Jones, who produced the band's Independent Worm Saloon album.