Is the Protector the item that evolves Rhyperior? If it's not, what is it? And where can I find it?
Yup, firstly it evolves Rhydon. Secondly, it is in the lower cave of Mt. Mortar. It requires Rock Climb to access it.
http://bulbapedia.bulbagarden.net/wiki/Mt._Mortar#Lower_Cave
