Miguel de Cervantes

In the prologue to Don Quixote, Miguel de Cervantes specifically states that he is not the author of the book which follows. Thus it's not as absurd as it sounds to investigate the possibility of a true, hidden author.

See also
:Dr. R. Langdon-Down's article on Shelton's Don Quixote and Francis Carr's table of similarities between Don Quixote, Shakespeare, and Bacon.