Pentagram can make the argument that they were one of the first bands to play what would become “heavy metal.” From their origins in 1971 playing hard cosmic blues in the vein of Blue Cheer, on through their doom-inflected heyday as Sabbath’s most legitimate competitor, Pentagram has remained an underground gem. Despite their rotating lineup, singer Bobby Liebling has kept the band going in one form or another, weathering trends and long recording droughts (including a 14-year gap between formation and their first album). Every doom metal band owes a significant debt to Pentagram.