Robert Plant. (Led zeppelin)
For his sheer uniqueness and clearness of voice, (yes ok the high pitch as well). And the fact that he can sing for ages on end solidly with no breaths.
Ian Gillan. (Deep purple)
For his ability to sing heavily and softly in the same verse and make it sound good, he can also bend notes to suit a song and it's emotions.
We are not retreating, merely advancing in the opposite direction.