[cincinnati65]

I seem to be the only one who remembers this, but when the original trilogy came out, Lucas explained that he shot Episodes 4 through 6, then would film Episodes 1 through 3, and finally Episodes 7 through 9, so Luke/Mark Hammill would have enough time to age naturally to play the villain in the final trilogy.

Shortly, thereafter, Lucas began saying that we were mistaken and that he never said he planned to do a trilogy of trilogies, but I swear I remember him laying this out during one interview.

[cincinnati65]

Also, remember....

"Fear is the path to the dark side. Fear leads to anger. Anger leads to hate. Hate leads to suffering.” -- Yoda

"You want this, don't you? The hate is swelling in you now. Take your Jedi weapon. Use it. I am unarmed. Strike me down with it. Give in to your anger. With each passing moment you make yourself more my servant."
Luke: "No." (swings at Emperor)
The Emperor: "It is unavoidable. It is your destiny. You, like your father, are now *mine*."

After Luke loses it and puts a beatdown on Vader, taking his hand.."You're hate has made you powerful. Now fulfill your destiny, take you're father's place by my side." -- Emperor

Truth be told, Luke's already turned.

[Dilbert San Diego]

My recollection is similar. I don’t recall talk of how Mark Hamill would age normally to play the part of Luke Skywalker in the future. But I do distinctly remember that Lucas said that the first three movies were the middle part of a nine chapter storyline.

[discostu]

Lucas’ story on that has changed a LOT over the years. Sometimes it was the middle of a trilogy of trilogies, sometimes it wasn’t. Sometimes they were all already written, sometimes they weren’t. Honestly I think he was making crap up, the Episode 4 thing in the crawl was really just a nod to the serials he loved and were ripping off the movie. Way too much of the story makes no sense at all if he’d already written it. Like the siblings thing, and Darth Vaders name and position (it’s pretty clear in the first movie Darth is his first name not some title, and he’s totally subordinate to Tarkin not the Emperors #2 guy).

In the books Luke went Dark Side a couple of times, but he kept coming back from it. They also developed this idea in the Clone Wars TV show that there’s a 3rd way with the Force, a group that’s not all goodie 2 shoes Jedi zen emotionless and also not slightly crazy all emotion Sith, Grey Jedi. Of course none of that is canon anymore.

[Gideon7]

It started with The Journal of the Whills (1973). Lucas reused portions of it for the prequels, especially episode 1.

http://starwars.wikia.com/wiki/Journal_of_the_Whills,_Part_I

[IYAS9YAS]

I seem to be the only one who remembers this, but when the original trilogy came out, Lucas explained that he shot Episodes 4 through 6, then would film Episodes 1 through 3, and finally Episodes 7 through 9, so Luke/Mark Hammill would have enough time to age naturally to play the villain in the final trilogy.

Bloom County took that on back in 1983. Funny, he was only off by a year (technically it was a prequels, not sequels): Jedi Knights don't wait 15 years for a sequel.