The most extensive argument that the King in _Huckleberry Finn_
was based on Emperor Norton appears in the book _Norton I, Emperor
of the United States_ by William Drury (Dodd, Mead, 1986).  Drury
partially bases his argument on the letter Twain wrote to
William Dean Howells on September 3, 1880.

The complete text of Drury's book (roughly formatted) is online at:

http://www.emperornorton.net/norton-drury.txt

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