Seth Clearwater is Leah's younger brother and a member of the La Push pack. He has sandy brown-colored fur. He transforms into a werewolf during the events of New Moon, around the same time as his sister, Leah. In New Moon and Eclipse he is shown to idolize Jacob Black, and is said to remind Bella of a younger Jacob. During the newborn attack in Eclipse, Seth stays with Bella and Edward, due to his young age of only fifteen, to act as a connection to the pack. 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. 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 joins him because he opposes Sam's plan to attack the Cullens. For most of Breaking Dawn, Seth is Jacob's second-in-command, until he is replaced by Leah at the end of the novel.
In 2010's The Twilight Saga: Eclipse, Seth will be played by Boo Boo Stewart.