Out of the loop. Can somebody explain who Clara, Max Gunther and Dan LeClair are?

I see these names a lot in connection to each other, and I know they have something to do with a book that was written in the 1980's and something to do with letters sent to the author, and now Clara is suspected to possibly be Barbara Dayton, and William J. Smith is maybe Dan LeClair. But it's all confusing to me, can somebody explain what all this is about, what's the deal with the letters, what's the signficance of the 1972 ad and 1982 calls, etc. Thank you.