When people think of history's greatest writers of mystery, many think of Sir Arthur Conan Doyle and his Sherlock Holmes' stories. And as it turns out, the highest-selling author of all time was a writer of mysteries. But it wasn't Conan Doyle. By sales numbers, the world's most popular writer is a different British mystery writer: Agatha Christie (1890-1976). Christie has sold billions of copies of her works, the most popular being her 66 detective vels and 14 short story collections (especially those featuring Hercule Poirot or Miss Jane Marple). Christie was also a well respected playwright, writing plays that have had long runs, such as The Mousetrap.