In the Knights of the Old Republic comic series, and in LucasArts' Knights of the Old Republic 1+2, which I have for the Playstation2, there used to be many Sith Lords. The Sith, the actual force-using anti-Jedi, were numerous in the old days of the Republic. They also had a lot of flunky soldiers and officers, etcetera. Many of these soldiers wielded blades imbued with 'Cortosis Ore', a rare mineral that naturally resists the blades of lightsabers, so the lightsabers cannot cut through them. If I rememeber correctally, they were called Sith Swords.
It was the infighting between all the Sith that caused Sith Lord Exar Kun to rule that there could be no more than two sith at any time. Infighting and blood feuds between Sith weakened their ranks, helping to bring them down, and make them vulnerable to the Jedi.
Eventually, if I remember correctally, Jedi named Nomi Sunrider, a cute redheaded Jedi Warrioress, actually slew Kun. Exar Kun is involved in the "Jedi Academy" series of Star Wars novels, where his spirit corrupts one of Luke Skywalker's powerfull students into killing many of people.