How did we miss this?
A week or so ago former Paragon devs have uploaded to Google Docs a copy of the fabled Lore Bible dated circa 2004. While much of the info is out of date it apparently contains the full backstory for Nemesis, the Rikti, Rularu, and other stuff.
Much of the history it contains has been retconned but the sheer volume of info should keep interested parties busy for weeks.
Go. Read. Kill skuls.