Question: who is the biggest selling author of all time
Answer: estimated sales Original language Genre or title Number of books Citizenship Christie , Agatha Agatha Christie 2 billion 4 billion English Whodunits including the Miss Marple and Hercule Poirot series 85 British Shakespeare , William William Shakespeare 2 billion 4 billion English Plays and poetry 42 English Cartland , Barbara Barbara Cartland 500 million 1 billion English Romance 723 British Steel , Danielle Danielle Steel 500 million 800 million English Romance 120 American Robbins , Harold Harold Robbins 750 million 750 million English Adventure 23 American Simenon , Georges Georges Simenon 500 million 700 millio