A bit more on Darth Vader as conceived in Oedipal terms: Freud stated that the Oedipus complex--the desire of the son to supplant the father--is connected to castration anxiety, the fear that the father will emasculate the son. Lucas has openly acknowledged that Luke's loss of a hand in his ESB duel with Vader was conceived as a symbolic castration scene.
It's interesting how all the Freudian imagery in the rough drafts of SW 1977 is connected with Princess Leia, whereas in the later films it revolves around Luke's father.
This dovetails with the fact that in the first film, Luke was meant to end up romantically linked with the Princess--whereas the subsequent films abandoned this and focused on Luke's discovery of his parentage, an idea not present in 1977.
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One thing in my initial post may actually be incorrect: the rough-draft Princess Leia's "long auburn hair tied in braids" was likely not yet based on the "buns" of Queen Fria from Flash Gordon.
Instead, Lucas may have had in mind the long twin braids of Princess Kriemhild from Fritz Lang's 1924 film Die Nibelungen.
Die Nibelungen is an adaptation in two parts of the medieval German epic poem known as the Nibelungenlied, which tells the story of Siegfried the dragon-slayer. Lang made it around the same time he made Metropolis, and like that film, Die Nibelungen is jam-packed with arresting visuals.
We know that Lucas was quite interested in Fritz Lang's early work: he borrowed from Metropolis not only the likeness of its robot for C-3PO, but also the Whore of Babylon motif for Princess Leia's disarrayed costume.
And we also know that Lucas was reading up on Norse mythology: he considered naming a planet after Brynhild the Valkyrie, a character in Siegfried's story, and Luke Skywalker's name comes straight from "Loki Sky-walker." So Lang's Die Nibelungen would have appealed to him on both counts.
In fact, the very name of the rough-draft hero, "Annikin Starkiller," may have been designed to evoke that of Siegfried/Sigurd, who slew the dragon Fafnir and was known thereafter as "Sigurd Fafnir's-bane."
(The Anakim were a race of giants from the Old Testament, so presumably Annikin's first name is meant to suggest strength and large stature, akin to that of the mythic Siegfried. However, the exact spelling used by Lucas at this time recalls the name of director Ken Annakin.)
Kriemhild is Siegfried's love interest in Die Nibelungen, so it would be fitting for Lucas to borrow her hairstyle for his princess character.
The probability of this connection is enhanced by other visual borrowings from Die Nibelungen which show up elsewhere in Lucas's work.
Take a look at Fritz Lang's Etzel, the barbarian king of the Huns:
Etzel's hairstyle is significant: it features a shaved head with a topknot and two long front locks.
The shaved head with topknot would recur in Moebius's concept art for Sorsha in Willow (a style recycled for TPM on Aurra Sing).
The shaved head and forelocks, on the other hand, would show up with the locks braided (recalling Kriemhild's hairstyle) in concept art for Obi-Wan's hairdo in TPM. (In the final film only one of the braids was used.)
Another of Lang's potent images in Die Nibelungen involves a connection between trees and death.
When Siegfried bathes in the blood of the dragon Fafnir, rendering him invulnerable, a leaf from a tree falls on his back, leaving one spot unmarked and thus open to attack. Later Siegfried finds the evil dwarf Alberich and slays him; in front of Alberich's cave there is a large tree.
When Siegfried makes a vow of blood-brotherhood with the Burgundian warriors Gunther and Hagen, who will eventually betray and murder him, they pledge their oaths in front of a tree. And when Siegfried dies, Kriemhild has a vision of a tree turning into a skull.
This motif would be reused in the script for ESB, in which a tree was placed at the opening of the sinister cave on Dagobah where Luke has a vision of Darth Vader.
The idea also apparently recurred in early concepts for Willow, where a magical tree with an interior of solid gold (an idea taken from the concealed gold in The Hidden Fortress) was located at the entrance to a dragon's cave.