Here are the most important facts about the book series Harry Potter:
1. Harry Potter is a series of seven books written by British author J. K. Rowling.  
2. The first book, Harry Potter and the Philosopher's Stone was published on June 26, 1997.
3. As of February 2023, more than 600 million copies of books were sold worldwide, making it the best-selling book series in history.
4. Although the book is aimed at a younger audience, the main themes of the series are death, prejudice, corruption, and madness.
5. Warner Bros. Pictures has taken the book and released a series of eight films.
6. In 2016, the total value of the Harry Potter franchise was estimated at $25 billion making Harry Potter one of the highest-grossing media franchises of all time.