In "Is Shakespeare Dead?" Twain entered the Shakespeare authorship debate with a bang. The work is pure Twain brilliance. Twain begins by listing the absolute known facts about Shakespeare of Stratford, which can fit nicely on one sheet of paper. He then examines the thousands of pages of Stratford Shakespeare biographies written by academics, and in his own hilariously sarcastic way mocks these "surmisers of surmised facts" explaining how they have inflated a "chipmunk's trail through Stratford" into a literary "Hercules" of renown.
Twain next speaks of "authentic authorship" by pointing out with convincing detail that unless you have walked the walk, you can't talk the talk. For example, he says Bret Harte attempted to write stories about life as a Mississipi riverboat captain or a sailor on the high seas, but that any real riverboat captain or sailor could tell in the first few lines that Harte was writing from book learning, not from actual experience as a captain or sailor. Twain nicely says that authors (no matter how brilliant) can't fake the language and tone of real experience when it comes to endeavors involving high levels of skill. You have to walk the walk to convincingly talk the talk. He then proceeds to point out one simple fact: the Shake-speare canon was written by a man who was deeply experienced in sixteenth-century law and legal procedures--as numerous legal historians of that period have attested--deeply experienced, not just a law clerk for a short period. Twain then proceeds to point out that not one shred of evidence exists that Stratford Shakespeare even served as a law clerk, let alone a deeply experienced barrister or judge.
Twain goes on in this vein in regard to the numerous aspects of Shake-speare's works that prove the author was a member of Elizabeth's court, was widely traveled, knew several languages, and was in actuality a Hercules of literary proportions, leaving us masterpiece after masterpiece, not the chipmunk who left his trail through Stratford.
Twain actually spends relatively little space talking about Francis Bacon as the author of the plays, despite what other reviewers seem to suggest, although this was Twain's belief at the time he wrote his book.
Twain, Freud, Washington Irving, William James, along with numerous others through the years have long been convinced that Shakespeare of Stratford was not the author of the plays. It has only been in the last 100 years though that a consensus has formed about who the author was. That consensus holds for Edward DeVere, Seventeenth Earl of Oxford. For an excellent book, among many, that DeVere was the author, see Mark Anderson's book "Shakespeare by Another Name." This is a highly controversial subject. For a book often praised that argues for the Stratford man as the real author, see Irvin Leigh Matus's "Shakespeare in Fact." After studying both, I am with Twain: the factual evidence is overwhelmingly minimal (still that one page and a lot of surmising) for the Stratford man, while the evidence for DeVere as Shake-speare is an avalanche of fascinating and convincing historical and documentary detail. Shake-speare is still alive, in the phoenix of DeVere.