About the Sith
The Sith is the only enemy of the Jedi. The Sith started out a race of people who lived on Korriban. They were a primitive race of people with the force being strong in their bloodlines, however they never practiced the force as the Jedi did. This week minded people came to worship the Dark Jedi who were exiled and discovered the planet and inter-breeding began. The name Sith changed after those people were "wiped" out. It became known that the Sith was a cult consisting of Dark Jedi (fallen Jedi Knights) that practiced and taught the ways of the Darkside of the Force.
Sith Lords and Apprentices