cmiller99
Super Freak
If we are leaving race out of it, because after Disney gutted the EU im not sure if the actual Sith race exists or not anymore, and we are going by a pure apples to oranges comparison... Sith is to Jedi style... Darth Vader was absolutely a sith lord and doing sith philosophy. Arguably as soon as he assisted unwittingly in Master Windu's possible (i still have hope) demise...
ill even go into further argument towards the fact he was in the OT, due to the fact that the return of "jedi" could not have happened.
What is the 'Sith order' in the PT? Two creepy evil guys, one has robes and one is half robot. They both use the dark side.
All the legends of the Sith Order, its history etc are all EU/PT additions. The OT barely touches on that. It's just good v.s. evil.
He wasn't a Jedi in the OT because he'd betrayed them all and killed them, as established by Ben Kenobi. That didn't make him a Sith though, and there's no specification in the OT that that is the case.