Dave,

Justin Kaplan's book is a good source of anecdotes
which suggest distinctive aspects of Clemens/Twain.

Be careful to avoid being seduced by all the funny
moments in his life lest you miss the sad times which
were equally, if not more, revealing of his essential
chracter.

In Kaplan's book there are particularly poignant
moments, such as when Clemens sang old gospel songs
when Livy died in Florence. Or when he waited
pathetically outside the hotel room of a young woman
who reminded him of Suzy (who was by then deceased).