The Gray Tusken was a member of the Tuskens, a para-military force in the Galactic Empire. He was one of a platoon sent down to the surface of Utapau by one of the Imperial officers aboard the captured rebel ship in orbit, in an effort to find out what Deak Starkiller was doing in the system.
This Tusken was a big, muscular man, with sunken, red eyes. His face was dusty.
When the "Gray Tusken" arrived at Anchorhead, he found a Mechanic who had already given Artoo and Threepio directions to the Lars homestead. The Tusken eventually followed Luke Starkiller and the droids into Mos Eisley.
Behind the scenes
The "Tuskens" became a native population on Utapau (later Tatooine) in the later third draft, and were no longer Imperial agents. That role was taken up later by the Desert Sands stormtroopers and by Garindan in the fourth draft (shooting script).