Samuel Clemens as Mark Twain was likely impersonated in the 1860's, and for
sure by the early 1870's (I have an original broadside for such a
performance).  The number of impersonations grew steadily, both legit &
outright fraudulent (charging $$ for bogus performances &/or
hotel/restaurant bills, etc.).

Similarly, Twain was used as a character in at least one book during his
lifetime.  THE LITERARY GUILLOTINE (1903 1st book publication) is the
earliest I have located, but let's not forget the first use of "Mr. Twain"
as a fictional character which was first published in Vanity Fair in 1861 by
A. Ward, not SLC (!!!). Then there is that elusive New Orleans use, as SLC
would refer to.

Twain has been featured in many, many shows, not the least of which is the
TV shows Bonanza, Star Trek, and Touched by an Angel.  My favorite reference
to Twain is the gift of Tom Sawyer as the ending of Its A Wonderful Life.

A ton of stuff can be drummed up with Twain as a fictional figure character,
and Twain's works dramatized, and even Twain dramatizing his works, etc.,
etc.,.  Best of luck to anyone who diligently researches and honestly
reports on this matter!

Best Regards,
Bob
www.MarkTwainCollector.com (&many others)