Classic metal isn’t a subgenre but rather an exclusive tier reserved for those bands that have attained universal reverence among the planet’s headbanging hordes. Needless to say, Black Sabbath, who more or less invented the genre, sit at the head of the table. Ditto for Judas Priest and Iron Maiden, who played central roles in transitioning heavy metal from its shaggy hippie roots into the screaming, classical-inspired beast that took flight in the ’80s. And the extreme end of metal’s spectrum has yielded a handful of immortals: it doesn’t get any more classic than thrash inventors Metallica and Slayer.