The Sith are people who are very self-centered and selfish. There used to be many Sith, but because they hunger for power, they killed each other off, so now there are only two - a master and an apprentice. Sith rely on their passion to get things done. They use their raw emotion, their hatred, their anger, their bitterness - which is the dark side of the Force. The Force is what binds the galaxy together, and it has a good side and a bad side. The Sith learned how to manipulate both sides of the Force, and then they fell into the trap of being corrupted by the dark side.
- George Lucas