Rick Riordan taught young adults and was already an author to mature novels but when his students asked to read his books he told them to wait until they were older then they went to the bookstore. The series had started as a story Rick Riordan made off the top of his head when his son asked to be told a story about the Greek heroes and demigods. He already taught it to students so he was happy to tell a story.However, when he ran out of ancient myths his son asked if he could tell a different story with the same characters.Upon hearing those words he remembered a creative writing project that he did with his sixth graders where they created their own demigods and made an adventure for them to endure. That became his inspiration for Percy Jackson the story of a demigod trying to find Zeus's lightning bolt in modern-day America.
The story was used as a bedtime story and took a whole 3 nights to fully complete however when he was done his son proposed he make a book out of it. Even though Riordan was preoccupied he found time and on February 10th 2009 the book was published.
He also says that he sees himself in Percy as he has his sense of humor and that Percy has the characteristics of some of his students.