Yes, technically there is a guy in a mask playing Tarkin in the closing moments of Revenge Of The Sith, but it doesn't really count. Grand Moff Tarkin is Peter Cushing and he was utterly brilliant as the ruthless commander of the Death Star in the original Star Wars film. What is so great about Tarkin is how cold he is towards his colleagues as much as he is his enemies. He has a power over Darth Vader that puts him almost at the same level as Emperor Palpatine, suggesting that he was very highly regarded in the Galactic Empire. He certainly isn't afraid to make controversial decisions; it isn't Vader but Tarkin that orders the destruction of Leia's home planet Alderann just to make a point. He would probably kill his own mother if it met his personal agenda. And of course, it is his superiority and arrogance that is his downfall. He refuses to evacuate the Death Star in his moment of triumph, even when his officer notes the small risk in the Rebel's attack and that leads to his dramatic death as the Empire's mightiest weapon is destroyed.