RicOlie_2 said:
I think Vader was always intended to be Luke's father though, even in the pre-ESB universe. His name even implies it.
*sigh*
Actually, Lucas' earliest surviving notes on Vader's name don't say anything about the word "father"--rather they suggest the name was a combination of the phrases Dark Invader and Death Water.
Also, I highly suggest you read through the Leigh Brackett script of ESB.