Straight from Gary Kurtz:

Gary Kurtz: “When we made Star Wars, Vader and Anakin were two separate people. The idea that Vader was Luke’s father didn’t exist. I remember Lucas talked about Anakin having killed Vader and then taking his identity, but that was dropped early on. The whole twist in Empire was new and unexpected.”

Star Wars Insider #138, 2011

I want to highlight this also because it pertains to something I think the posters here need to remember when posting their opinions in this thread: Whatever our personal opinions or feelings, facts are facts. I’m saying this applies to most of the past posters in this thread, myself included. I can freely admit when I’m wrong, and I was wrong thinking that Lucas made ANH(STAR WARS 1977) with the intention that Vader was Luke’s father (Annikin), and that Luke and Leia were twin siblings. Gary Kurtz - pertaining to the facts of the matter - is a test-control or verification check on Lucas’s claims, whether as a corroboration of them or a refutation of them.