Sprung from the roots of 70s hard rock, Metallica defined the look and sound of 1980s heavy metal, just as Led Zeppelin had for hard rock and the Sex Pistols for punk before them. Inventors of thrash metal--Slayer, Anthrax and Megadeth followed--it was always Metallica who led the way, who pushed to another level, who became the last of the superstar rockers.