Oh My Lord..
That man can sing. He has been my favorite singer for a while, there is just no one that ever could, can, or will ever sing like him I don't think. It didn't matter what he sang or how he sang it. It was just pure magic. He set the bar in terms of scream-singing with his crude and gut wrentching yet tasteful and perfectly executed vocals. My favorite performance from him would have to be "Since I've Been Loving You"--pure Robert Plant magic. In fact I'm totally going to go listen to it right now.
Not only is he one of my few true rock heros, but he is arguably the greatest and most influential vocalist in Rock history. (Though I would actually argue that Freddie Mercury was the most skilled--sorry Plant!)