In the third book, Seth is the youngest werewolf to fight with the Cullens, Jacobs nickname for him is "Kid", he thinks werewolfs can be friends with vampires and he doesnt call them "Bloodsuckers" or any of the names the wolfs call them, he calls them all by name. Seth the playful, loving little brother that becomes great friends with Edward when they battled with Victoria. He also help protect Bella and unborn Renesmee in Breaking Dawn.
He is tall "gangly", with sandy hair and and dark brown eyes.
He is also sandy color as a wolf too.