After Black Sabbath fired Ozzy Osbourne, their next move was a make-or-break affair. The decision to hire Rainbow/Elf vocalist Ronnie James Dio and proceed in a more “dungeon metal” direction paid off handsomely with this mostly-downtempo epic. The song’s driving vibe was carried onward by both Sabbath and Dio after their separation, and was returned to in glorious fashion when they reunited as Heaven & Hell in the late 2000s. – Peter Hodgson