Buffy the Jedi Master.
In the decades since Star Wars changed the world in 1977, a wealth of material about the saga's developmental stages has come out, with some bits of old concept art and words like "Starkiller," the original last name for Luke, even getting repurposed in later chapters and the extended universe. The Making of Star Wars: The Empire Strikes Back, by J.W. Rinzler, is a fantastic resource filled with a ton of surprising facts, such as the original name for Jedi Master Yoda. It was Buffy. Yes, Buffy. In early outlines drafted by George Lucas, Bunden Debannen aka Buffy was three to four thousand years old. Luke, the Chosen One, would be "the human buffy." Later, Lucas envisioned him as a frog type creature, with the full name Minch Yoda.
The Emperor wasn't always played by a man.
Before the great Ian McDiarmid was retroactively inserted into later editions of The Empire Strikes Back, to tighten up continuity with Return of the Jedi and the Star Wars prequels, actor Clive Revill voiced the mysterious and decrepit leader of the Galactic Empire. But it was a woman named Elaine Baker underneath the makeup. She was then the wife of Academy Award winning makeup artist Rick Baker, who in addition to his work on Star Wars, worked on An American Werewolf in London, Coming to America, the Men in Black series, and Michael Jackson's Thriller. Baker not only made the suit for the 1976 King Kong movie, he's the guy inside of it! Speaking of primates, Elaine Baker's eyes in Empire were the eyes of a chimpanzee.
Darth Vader wasn't always a Skywalker.
In the first draft by the late Leigh Brackett, aka the Queen of Space Opera, Anakin Skywalker, Ben Kenobi, and Minch Yoda swear Luke into the Jedi Order, in a little ceremony that involves an oath and the crossing of their lightsabers. Anakin also tells Luke about his sister, who was also training to become a Jedi, just like Luke.
Leia wasn't always a Skywalker either.
That sister in the early drafts was not Princess Leia Organa of Alderaan. In the second draft of The Empire Strikes Back, Vader tells Luke, "You're in love with Leia. You don't want to lose her to Han Solo... But you will, if you lack the courage to use the strength that's in you. A strength as great as mine, Luke." This second draft and its accompanying dialog, which of course reads much differently with the addition of the now familiar familial twists, was written by George Lucas himself.
George Lucas always had a Harrison Ford back-up plan.
Before anyone knew whether or not the first Star Wars would be the kind of success that could warrant a big budget sequel, Lucas commissioned a novelist to write a story for a sequel that could be made for less money, reusing sets, and without Harrison Ford, who wasn't signed on for follow-ups. Splinter of the Mind's Eye featured a Luke and Leia romance, as the shipwrecked duo searched a swamp planet for something called a "Kaiburr crystal." Both Luke and Leia would've had lightsaber duels with Darth Vader. In a similar fashion, the whole "frozen in carbonite" plot device was cooked up as a way to write Han Solo out of the next movie should wily scoundrel Harrison Ford have chosen not to return for a third Star Wars movie. (Of course, we all know what happened when Ford agreed to make The Force Awakens.)
Darth Vader's Castle.
The Empire Strikes Back nearly included a glimpse of the place Darth Vader calls home. Molten lava would have surrounded this castle-like fortress. Eventually, we saw a version of this in Rogue One: A Star Wars story, built with bitter sentimentality on Mustafar, near the site of the battle where the young Sith Lord nearly lost his life to his old master, Obi-Wan. In some versions, Vader had pet gargoyles. It's possible this was an inspiration for the pet seen in one of the best episodes of TV's excellent The Clone Wars series, "Lair of Grievous." Poor Gor, may that guard beast rest in peace.
Darth Vader spoiled Empire two years earlier.
Fans who picked up a CD copy of John Williams' score for Star Wars Episode I: The Phantom Menace, before they saw the movie, were treated to songs with titles like, "The Death of Darth Maul," "The Death of Qui-Gon," and "The Funeral of Qui-Gon." A 1978 newspaper report quoted David Prowse, the man in Darth Vader's suit, as saying, "Father can't kill son, son can't kill father," in front of 1,000 fans during an appearance in Berkeley, California, where he openly discussed Vader's link to Luke. The reveal was spoiled again for anyone who picked up the novelization of Empire, which was released a month before the movie. Speaking of that reveal, even Chris Farley got the line wrong. It isn't "Luke, I am your father." It's, "No, I am your father."
Attack of the Calrissians.
At one point, wily scoundrel and Han Solo best frenemy Lando Calrissian was conceived as a clone, from one of many warrior clans left over from the Clone Wars.
Attack of the Wampas.
That killer snow beast on Hoth who feels like a distant cousin to the Abominable Snowmonster of the North from the Rankin/Bass Rudolph the Red-Nosed Reindeer television special was originally supposed to have a bunch of friends. Unfortunately, they just couldn't get the creature to look believable enough with the effects of the day, which is why the original theatrical cut of The Empire Strikes Back only shows the Wampa's hand and head. As a result, the production scrapped a planned scene where a whole pack (or is that herd?) of Wampas would have attacked the Rebel base, doing considerable damage to the Millennium Falcon in the process. This would've explained why the Falcon was always falling apart for the rest of the movie. Instead, filmmakers decided to put that on the ship's general wear and tear.
Mark Hamill regrets Empire's animal cruelty.
No Earth animals were hurt on the set of The Empire Strikes Back, but we do know of at least one snow beast from the planet Hoth who lost a limb. In a reply to a fan who Tweeted him a picture of a cake shaped like a severed wampa arm, shortly before the release of The Last Jedi, Hamill revealed a bitter truth. "When filming scene I was assured my lightsaber swipe toward camera (creature not on set) would simply singe fur 2 scare him off - Horrified to later see amputation & unnecessary cruelty, Wampa was HUNGRY (not EVIL), Luke would never do this! #StillAngry2017".
When filming scene I was assured my lightsaber swipe toward camera (creature not on set) would simply singe fur 2 scare him off-Horrified to later see amputation & unnecessary cruelty-Wampa was HUNGRY (not EVIL)-Luke would never do this! #StillAngry2017https://t.co/QhIkOILZmw— @HamillHimself (@HamillHimself) November 27, 2017