Mark comments in Chapter 22 of Life on the Mississippi "... wicked
impostors go around lecturing under my nom de guerre and nobody suspects
them; but when an honest man attempts an imposture, he is exposed at
once."  

I was just wondering what documentation might exist as to the number of
people that may have been "lecturing under my nom de guerre".  And, who
these people might have been.

It appears he was then and continues to be someone to be portrayed.