Portrayed by Boo Boo Stewart
Seth Clearwater is Leah's younger brother. He transformed into a wolf during the events of New Moon, around the same time as his sister, Leah. He has sandy-colored fur, and at 15 he is among the youngest of the pack. In New Moon and Eclipse he is shown to idolize Jacob Black and is said to remind Bella of a younger Jacob. Like Quil, he is excited by his ability to transform into a wolf and not unhappy with it, as his other pack brothers are. During the newborn attack in Eclipse, Seth stays with Bella and Edward due to his youth and acts as a connection to the pack because of the wolves' telepathic ability. When Victoria and Riley appear, Seth fights and destroys Riley with Edward's help. In Breaking Dawn he is shown to have developed an unlikely friendship with Edward, and attends his and Bella's wedding. Seth remains a constant presence throughout the final book in the series. He is initially the only wolf to feel completely comfortable being around the Cullen family, and becomes friendly with them by the end of the series.
Although young, Seth appears to have sharp mind and quick thinking as he was the first to oppose the assault towards the Cullens because the pack refused to consult with the Elders (which they were supposed to do and initially aborted the mission due to lack of offensive force) and he was the first to recognize that Jacob isn't thinking properly when he wanted to attack the Cullens after Bella's arrival from Brazil due to the treaty without proper investigation. Seth was also the first one to discover that different pack has their own mental link and convinced both Jacob and the Cullens that Sam's pack will not launch an assault due to lack members because it will be a suicide mission for Sam if he did. He also has, according to Edward, very honest and pure thoughts, something that endears him to the Cullens, and Edward in particular. When Jacob splits from the pack, Seth quickly joined him because he opposes Sam's plan to attack the Cullens, whom he has become fond of. For most of Breaking Dawn, Seth is Jacob's second-in-command, until he is replaced by Leah at the end of the novel.