Original: On his eleventh birthday, Harry learns from a mysterious stranger, Rubeus Hagrid, that he is actually a wizard, famous in the Wizarding World for surviving an attack by the evil Lord Voldemort when Harry was only one year old.
Simplified: On his eleventh birthday, Harry learns from a mysterious stranger, Hagrid, that he is actually a wizard, famous in the wizarding world for surviving an attack by the evil dark Lord Voldemort, when Harry was only a year old.