There are many theories about the true identity of Shakespeare. A new one (at least, new to me) is that Shakespeare was actually a Jewish woman named Amelia Bassano Lanier. This argument is made by John Hudson, author of a forthcoming biography of Bassano (who was the first woman to publish a book of poetry in England). Haaretz reports:
The theory rests largely on the circumstances of Bassano's life, which Hudson contends match, much better than William Shakespeare's did, the content of "Shakespeare's" work. But Hudson has also identified technical similarities between the language used in Bassano's known poetry and that used in "Shakespeare's" verse. And he has located clues in the text - recently noted Jewish allegories and the statistically significant appearance of Amelia Bassano Lanier's various names in the plays - that he says point to her as the only convincing candidate for the author of Shakespeare's work.
If it turned out that Shakespeare really was a woman, that would top Pope Joan for Most Outrageous Case of Gender Concealment Ever. However, I'm sure that mainstream Shakespeare historians are going to resist accepting Hudson's theory.