[Urwen]

Okay, then one must be Tar-Miriel, who was used by Pharazon so he could obtain the throne which wasn't his.

For the other, I am drawing a blank. Morgoth, who used Hurin, Maeglin and the House of Ulfang for his evil purposes comes to mind, and he did desire vengeance, but, as Huinesoron pointed out, none of them was completely benevolent.

Then there is Sauron, who more or less used Denethor and Gollum, but again, neither of them were completely benevolent.

(In fact, the only person who could reasonably be called 'pure' is Frodo, who resisted the lure of the Ring for the longest time, only to succumb at the end. But he wasn't really 'used' by anybody.)

Lotho comes to mind. We don't know much about him, except that he was used by Saruman as a puppet ruler, and then killed on his orders.

So Tar-Miriel and Lotho are my guess.