De Wikipedia: Franklin W. Dixon is the pen name used by a variety of different authors who were part of a team that wrote The Hardy Boys novels for the Stratemeyer Syndicate (now owned by Simon & Schuster). Dixon was also the writer attributed for the Ted Scott Flying Stories series, published by Grosset & Dunlap.
Canadian author Charles Leslie McFarlane is believed to have written the first sixteen Hardy Boys books, but worked to a detailed plot and character outline for each story. The outlines are believed to have originated with Edward Stratemeyer, with later books outlined by his daughters Edna C. Squier and Harriet Adams. Edward and Harriet also edited all books in the series through the mid-1960s. Other writers of the original books include MacFarlane's wife Amy, John Button, Andrew E. Svenson, and Adams herself; most of the outlines were done by Adams and Svenson. A number of other writers and editors were recruited to revise the outlines and update the texts in line with a more modern sensibility, starting in the late 1950s.