Probably the most underrated vocalist - period. I remember listening to Butterfly Ball when I was a child.
During the MTV years when Metal was saturating the market, his band wrote some brilliant music.
But my favorite Dio album was definitely his years in Black Sabbath. Neon Knights is an undisputed classic.
Sadly missed, but will no doubt be jamming with Randy Rhoads, Phil Lynott and John Bonham.
