The Letters Of Mark Twain, Volume 4: 1886-1900 Mark Twain's Letters is a collection of the written letters by the famous American author and satirist Mark Twain, the pen name for Samuel Langhorne Clemens. The letters are a detailed insight to the mind and personal life of Twain in such a way not revealed in any other sense. They are a definitive collection of nearly all of Twains letters.