Twain bequeathed to history much more than “a signature or two.” In addition to a whole archive of notebooks, articles, and unpublished or unfinished manuscripts, he dictated half a million words of autobiography, and he appeared in public so often that even if he’d never written or dictated anything, many thousands of others could have supplied accounts of his existence. Chernow is the latest in a long line of biographers undaunted by this surplus of Twainiana (a line so long, in fact, that he is not even the only recent biographer named Ron).