Another country heard from:

It strikes me that in "The Man *Who* Corrupted Hadleysburg," the focus of
the title is on the man.  I.e., it is his story.

In "The Man *That* Corrupted Hadleysburg," on the other hand, the focus of
the title shifts to the act of corruption itself -- which, of course, is
as it should be (the man being more agent than character).

It's interesting to contemplate whether Twain actually gave conscious (or
unconscious) consideration to the whether of "That" or "Who."
Even if he gave a lot of thought to the issue, however, I tend to agree
with the contributor who suggested he'd be laughing himself silly right
now.

                        Larry Doyle