Sleep's 1991 debut, Volume One, displays the heavy influence of doom metal forefathers like Black Sabbath, Witchfinder and Saint Vitus. Driven by Matt Pike and Justin Marler's lumbering mass of low-tuned guitar riffs, Al Cisneros' serpentine bass and ragged screams, and drummer Chris Haikus' kit-pummelling, Sleep's rhythm guitars would never again be kept as under control, nor would their leads sound quite as refined as they do here (see the cleaner harmonies employed to good use on 'Numb' and 'Catatonic', for example).