I submit (controversially) that just as Jesus was not himself a Christian, Black Sabbath was not a metal band. They opened a cosmic door when they dropped their tuning and produced some of the most earth-splittingly heavy riffs ever recorded, but they did that as a classic rock band operating in a classic rock context. Led Zeppelin and Blue Öyster Cult likewise pushed the limits of how hard a rock band could rock, but didn’t quite break them. I personally draw the metal line at Mötorhead’s formation in 1975; it took a maniac like Lemmy to cross the threshold...