Governor Tarkin. I should have expected to find you holding Vader's leash. I detected your foul stench when I was brought on board.
-- Leia Organa
Grand Moff Wilhuff Tarkin is an influential figure in the Star Wars universe, and a key character in A New Hope.
Tarkin was born on Eriadu, and quickly became a powerful player in that region's military and government. He was disillusioned with the state of the Republic, and kept a sharp eye out for opportunities to become part of a new order.
By the time Senator Palpatine began implementing his own plan for the galaxy, Tarkin was very well connected. After demonstrating his loyalty and resolve by killing hundreds of rebellious protesters on Ghorman, he was awarded command of the entire Seswanna sector.
In the early days of the Empire, the fledgeling Rebellion forces were easily able to evade their opponents by moving across sector boundaries. The political structure of the Empire at the time meant that officials weren't inclined to pursue rebels into other sectors. Tarkin suggested an effective countermeasure — create overlapping priority sectors, the size of which depends on the amount of sedition in the area. The overseer of each sector would be the "Grand Moff," and thus Tarkin became the first to hold that title, supervising a huge territory in the Outer Rim.
Tarkin was also instrumental in the creation of the Death Star, and the paradigm which led to it. The "Tarkin Doctrine," or the doctrine of fear, held that the most effective way to control all the systems under Imperial rule would be to evidence a single, monumental threat. The Emperor adopted this doctrine as the Empire's new subjugation policy, and placed Tarkin in charge of realising that policy. When the physical manifestation of the doctrine of fear — the Death Star — was completed, Palpatine disbanded the Senate. Tarkin ordered the destruction of the planet Alderaan as the first demonstration of the station's capability.
Tarkin was killed when the Rebellion's desperate attack on the Death Star at the Battle of Yavin succeeded.
Tarkin was played masterfully by actor Peter Cushing in A New Hope, and in many ways his character acts as a symbol for the Empire as a whole. Sneering his way from scene to scene, Cushing portrays a gaunt, ruthless and implacable being entirely without compassion or regard for human life. His only interest is power, and any means is justified. The characterisation is as believable as it is despicable, and creates a visible enemy for the audience — this is what we're fighting against.
In Revenge of the Sith, a younger version of the character was played by Wayne Pygram.