Via Starwars.com:

Welcome to From Concept to Screen, an ongoing article series about the various stages of the production that your favorite character, vehicle, creature, location, or scene of the Star Wars saga had to undergo before arriving on the silver screen.

We start this series with the main character of the movies, the man whose story the saga is all about, the menace in black: Darth Vader.

Idea & Concept

Considering the importance of Darth Vader in the saga, it will come as no surprise that he was always in the script in some shape or form. Before working on the rough draft, Lucas started making lists of the various ideas he had written down before in the Journal of the Whills (a two-page idea fragment) and The Star Wars treatment (dated May 1973, this is a 14-page treatment that evolved from the Journal of the Whills), and one of the names he had listed down was a General Vader, an Imperial commander. In The Star Wars rough draft summary from May 1974, this character was a bit fleshed out and described as “Darth Vader, a tall, grim-looking general”; he is tasked to conquer Aquilae.

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