Who is Sam from Eclipse and what is their importance?

Sam is the leader of the werewolves. Sam was the first to transition after a generation of Quileutes failed to become werewolves. For this reason, Sam was not prepared for what happened to him. To add to this, Sam was in love with a young woman named Leah, but after he transitioned into a werewolf, he imprinted with Leah's cousin, Emily. This caused a great deal of heartache for Leah and created a precedent for the other werewolves that some of them have come to dread. Sam is not the true leader of the werewolves, but accepted the leadership when Jacob refused it.