I think the origins of “Father Vader” are probably even simpler than Kiminski’s theory once you take what we know of Star Wars’ development into account.
The Star Wars that hit theaters functions mostly as a standalone story, Lucas having “stolen the ending” of the two-parter he’d had in mind and ending up with a movie that in the broadest strokes resembles what’d become the overall trilogy in condensed form, and there’s really only a few major plot points it didn’t cover, two of the biggest ones being:
- The hero’s cyborg father makes a heroic sacrifice
- The “black knight” villain turns against the empire and saves the heroes
With that in mind, when you hear the way Lucas puts it in the “From Star Wars to Jedi” doc from 1983: (https://youtu.be/YKhGkiHSlAA?t=3292)
“As that evolved as I did the first film, I didn’t know how the public would take all this and that it would be as successful as it was and Darth Vader would become the character he became. And so when I got down to the second film, I had to make a decision about whether I was really going to go through with this thing, of him being his father. And I finally decided that that really was the way, that was the original story and that was the one I really liked the most and so I had to stick with it.”
Yes, Lucas is still being cagey here and I’m sure he’s hoping people will take it that a Brilliant Plot Twist was always the plan… but strictly speaking, what he’s saying fits right in line with what we know. He had an opportunity to go back and tell “the original story” involving a cyborg father and a heroic sacrifice, because (completely serendipitously) the “black knight” villain had become the cyborg.
This is the storyline he “liked the most” over the one that moved the father’s death into the unseen past, the latter of which sounds exactly like the kind of compromise you make when you’re trying to shove everything back into a single movie (Obi-Wan Kenobi’s death would sort of serve as a substitute, though that was also entirely serendipitous - Obi Wan was going to live to the end but it was Marcia’s suggestion that he be killed off).