There being some kind of cosmic rule that I am only given subjects to
write on, about which I know nothing, would the members of this forum be
so kind as to recommend those biographical works essential to
understanding Twain?

I've only got three at hand: Rasmussen's Facts-on-File one-volume /Mark
Twain A to Z/; Kaplan's biography, and Emerson's /Mark Twain: A Literary
Life/.

I'm looking for sources that are as detailed, and specific , as possible.

Another question, please: other than the Mark Twain Letters & Project,
what other on-line sources might be helpful?

My emphasis, God help us, is biographical, as compared to say, literary.

Thank you!

Cordially,
Sara