The Official Star Wars The Old Republic site has revealed
what was already a bit of a no-brainer, but officially
there will be a Sith Class for the upcoming BioWare MMO.
An unstoppable force of darkness, the Sith Warrior is entrusted with the task of destroying the Empireís enemies and enforcing Sith domination across the galaxy. The Warrior channels the destructive emotions of fear, anger, and hatred to purge weakness from body and mind and become a being of pure, brutal efficiency.
If you check out the link above, there are three very, very short videos showing off some of the Sith's powers, but it all still looks very cool. The Sith Class is the fourth announced Class for the title alongside The Smuggler, Trooper and Bountey Hunter classes.