Astrid Ellison is a 14-year-old resident of Perdido Beach, and is the elder sister of the severely autistic 5-year-old, Little Pete, known as 'Petey'. She is commonly known as 'Astrid the Genius', on the part of her being in all the AP classes Perdido Beach School offered, as well as taking part in online university courses. She is the sometimes girlfriend of Sam Temple.
Astrid is a slim girl with shoulder length blond hair and blue eyes. She liked to wear starched white short sleeve blouses, but then moved onto t-shirts. Sam describes her as being way out of his league, so is a pretty girl.