Sam Uley is a La Push werewolf, or shape-shifter. He is the great-grandson of Levi Uley,one of the Elders of the Quileute tribe, and the son of Joshua Uley and Mrs. Uley. He is the Alpha of his pack. Sam was the first of his generation to turn into a wolf.
 Book Mentions
Sam was mentioned in Twilight as a teenager who came to First Beach in La Push and talked to Bella and her friends, talking about the Cullens. This caused Bella to weasel the story out of Jacob, about the Cold Ones.
In New Moon, Sam took on the role of Alpha, leading the ever-growing pack and teaching them the ways of the wolf and helping them to get used to their new life. To Bella and Jacob, before he phased for the first time, it seemed as if he had started a cult. When Jacob phased, it was Sam who gave him the command not to inform Bella. The members of a pack must follow the commands an Alpha gives, or suffer serious pain and mental shacklement. Once Bella found out the truth, Sam accepted her help with the search for Victoria.
In Eclipse, the pack and Sam help out in battling Victorias army with the Cullens, partaking in 'booster classes' on how to kill a vampire, taught by the military Jasper. When the Cullens chase Victoria to the border between La Push and Forks, Sam and his pack attempt to attack her, but she manages to slip away.
In Breaking Dawn, when Jacob tries to get the pack to kill the Cullens in the belief that Bella has become a vampire, Sam refuses to attack, stating that she chose to become one. But when Jacob comes back with the news that Bella is pregnant with the hybrid Renesmee, Sam decides to lead the pack in attacking the Cullens and killing Bella and the baby. Jacob refuses to attack, as does Seth, but the Alphas commands bid them to. Jacob decided that he would become the Alpha, since it was in his blood, but he didn't want to be it when the pack started out. Jacob split off from Sams pack, and later, so did Seth and Leah Clearwater. Later, when Renesmee was born, Jacob was enraged, and decided he was going to kiill her himself. When he saw Renesmee, he imprinted on her, causing an unlikely truce with the Cullens, since it was extremely wrong to kill an imprintee of a pack member.
Sam is described as having black hair, a very deep voice, an older face, copper skin, cropped black hair and brown eyes. Like the other werewolves in human form, Sam is described as being quite tall. In the New Moon movie, Sam is shown as having a tattoo on his shoulder, a mark that he is a member of a pack. As a wolf, Sam is described as having black fur. He is huge, quiet as a shadow, tall as a horse but more muscular, with dagger-like teeth.