Planning for both "The Lightning Thief" and the series began when Riordan started making up stories for his nine-year-old son, Haley. He had started studying Greek mythology (stories) in second grade. He wanted his father to tell him stories about them before he went to sleep. Riordan had taught Greek myths as a middle school teacher. He remembered some of the myths, which he then told to his son. Soon, Riordan had told him all the stories. When Haley wanted him to make up new stories using the characters from the myths, Riordan created the character of Percy Jackson. Like Percy, Haley had ADHD and dyslexia. He made up the story of how Percy traveled across the United States to search for Zeus' master bolt. After hearing the story, Haley wanted his father to write a book about Percy and his friends.