Robert Hilliard is a Ravenclaw prefect. He writes a letter that newly sorted Ravenclaw’s receive to learn more about their Hogwarts House.
Robert Hilliard was the prefect Rowling created to welcome anyone who got sorted into Ravenclaw on the website once known as Pottermore. Pottermore no longer exists, and any writings that Rowling posted there can now be found on the Wizarding World website. However, this editor could not find any reference to Hilliard on the updated Wizarding World website. --EJ