 Throughout the series Buffy Summers ( Sarah Michelle Gellar ) , in her role as the Vampire Slayer , is assisted by her close friends , who refer to themselves as the " Scooby Gang " . These include Xander Harris ( Nicholas Brendon ) , a young man without particular strengths or talents , but devoted to Buffy and her calling , and Willow Rosenberg ( Alyson Hannigan ) , a young woman who has grown from a shy but gifted student into a strong woman and powerful user of magic . They are mentored by Buffy 's " Watcher " , Rupert Giles ( Anthony Stewart Head ) , a paternal figure since the first season , when Buffy moved to Sunnydale after her parents ' divorce . Xander is engaged to Anya Jenkins ( Emma Caulfield ) , a former vengeance demon who has become human . They have struggled with disclosing their engagement to the rest of the group and individually doubt their impending marriage . 
