Why another book about Mark Twain? There are 20 biographies about him and I've read several, including his autobiography. More has been written about Samuel Clemens than any other American writer.
Well, he was just damned interesting: a Confederate militia member (for 2 weeks), a riverboat pilot, a prospector, a lecturer, an inventor, a humorist, a journalist, an investor, a travel writer, among other occupations. And, since 1966 more than 5,000 of his letters have been discovered.
Twain was a prolific writer and often reworked earlier tales of his. Near the end of his life, he extended his writing beyond the humor for which he is known into areas of politics, being strongly critical of western imperialism and the Catholic church.
As an investor, he was a disaster. That his family had any assets left at all is due to his meeting one of the former Standard Oil vice-presidents, Henry Rogers, who helped him with investments. Twain had sunk hundreds of thousands of dollars into a typesetting machine, the Paige Compositor, and continued to throw good money after bad until Rogers began to monitor investment contracts with the inventor. Rogers was too late to help him with the publishing company that Twain ran with his nephew, the Charles L. Webster Co., which eventually went bankrupt despite having Clemens' titles and books by Pres. U.S. Grant, Gens. Phil Sheridan and William Sherman, Leo Tolstoi and Walt Whitman's biography.
Interestingly, though Thomas Edison is known to have made several recordings of Samuel Clemens performing as Mark Twain (and possibly even a brief film), none are known to exist. Perhaps with the recent discovery of an old wax cylinder of the voice of Alexander Graham Bell in 2013, one will yet be found.