imperialscum said: Why prequels? Although not said on screen, Vader and Palpatine were Sith in OT... long before the prequels came out. Then TOTJ made a story where Sith became red skinned aliens. Someone had to connect the dots then. TOR did it pretty well.
TOTJ and KOTOR connected the same dots much better. Both TOTJ and KOTOR explained that the influence of Freedon Nadd, Exar Kun, Revan, etc. caused the Sith to stop being red-skinned aliens.
On another note, when Lucas said that anybody can use The Force in 1981, it was in response to the question of whether or not Palpatine was ever a Jedi. The implication is that Palpatine isn't a Sith.