Sam was the first of the boys from the reservation to phase and become a werewolf. The first time he met Bella Swan, he said that the Cullens were not welcome at First Beach, which sparked the conversation leading Jacob Black to tell Bella about vampires and werewolves.
As the other boys on the reservation became werewolves one by one, Sam took on the role of Alpha and led them through their change and helped them become accustomed to their new life. To outsiders, it seemed as if he had started a cult. When Jacob became a werewolf, it was Sam who gave him the injunction (an absolute command given by the Alpha) not to tell Bella. Once Bella figured out the truth, Sam accepted her help with the search for Victoria.
In Breaking Dawn when Jacob tells the pack that Bella is having a baby, Sam declares that they have to kill the fetus, and Bella along with it, as a necessary casualty to protect the tribe. Jacob embraces the Alpha heritage in his blood and he, Seth and Leah Clearwater leave the pack so they can protect the Cullens. Sam concluded that if Bella was killed, Jacob would be so mad that he would lead both packs in attacking the child. This never happened: Jacob wanted to kill Renesmee, but imprinted on her once he saw her. Sam and his pack were left with no choice but to declare true peace with the Cullens.
Sam and his pack later stood by the Cullens when the Volturi confronted them. After the incident, Sam and his pack returned to La Push.
* Leah Clearwater
Sam and Leah were dating throughout their high school years and were very close despite the fact that Sam turned into a werewolf and could not tell Leah. Their relationship ended when Leah brought her cousin Emily Young down for a visit and Sam imprinted on her. It is revealed in Breaking Dawn that Sam still loves Leah and begs her to come back to his pack after she runs away to Jacob's renegade pack with her brother, even asking his messenger, Jared, to 'go on his knees' and call her Lee-Lee, his old nickname for her which angered her to no end. They are the couple that can never be
* Emily Young
Emily young is Leah Clearwater's cousin and is engaged to Sam Uley.
After becoming a shape-shifter, Sam imprinted on Emily, and at some point before New Moon they became engaged. She was furious at first, but she was meant to be with Sam, and fell in love with him. One night, Sam lost control of his anger and accidentally hurt Emily, leaving her horribly scarred on her face and hand. Despite that, Sam loves her unconditionally, but has never forgiven himself for being so careless.
* Physical description
As a wolf, Sam is described as having black fur. He is huge, but as quiet as a shadow, as tall as a horse but more muscular, dagger-like incisors. He has a grisly snarl and is very swift.
As a human, Sam is described as having long, rounded muscles, a deep voice with an older face, copper skin, very tall, cropped, black hair, and brown eyes.
* Movie portrayal
Solomon Trimble was credited as "Jacob's Friend" in the Twilight movie , but said what Sam had said in the book.
Chaske Spencer will be playing Sam in the upcoming New Moon movie.