Tom Morello. I remember listening to the first RATM album and being suitably impressed, then reading the inlay and completely refusing to believe there were no synths or samples used during recording. I've seen them either side of the split, and the thoughts that persist in my head are 'HOW? HOW?'

Other notables would be Kirk Hammett and Billy Corgan (if you'll forgive shoehorning some hard alt-rock into a metal nominations list).