Summary
According to Darth Plagueis, thirty Sith Lords existed in the time between the Seventh Battle of Ruusan and the rise of the Sith during the Battle of Naboo. Yet we dont know who these Sith are. But now, here is a complete history of the various Sith Lords, who's millennia of scheming allowed for the Sith to destroy the Republic and eradicate the Jedi