Months prior to the film's release, John Williams was named Conductor of the Boston Pops Orchestra. During Williams first televised performance with the Orchestra on PBS's Evening At Pops, he publicly premiered some of the new scoring pieces he composed for the movie.
During the filming of the Battle of Hoth, the Echo Base troops were actually Norwegian mountain-rescue skiers. In exchange for participation in the film, Lucasfilm made a donation to the Norwegian Red Cross
When Han Solo is about to be frozen, Princess Leia says, "I love you." In the original script, Han Solo was supposed to say, "Just remember that, Leia, because I'll be back," but at the time of filming, Harrison Ford wasn't entirely certain he did want to come back for a third film. There is a recurring legend that his line, "I know", was ad-libbed; however Alan Arnold's book "Once Upon A Galaxy: A Journal of the Making of The Empire Strikes Back" includes a transcription of the discussion between Ford and Irvin Kershner in which Ford suggested the line.
In order to avoid sharing creative rights, George Lucas decided to avoid using a major studio to finance this film. Instead, he bankrolled the $33 million production himself, using a combination of his profits from Star Wars: Episode IV - A New Hope (1977) and a bank loan. Although the move was risky, it paid off several times over. Lucas recovered his million investment within three months of the film's release. He then showed gratitude far beyond the Hollywood norm, by sharing the profits with his employees (nearly $5 million in bonuses).
In the asteroid scene, one of the asteroids is actually a shoe. The rumor is that George Lucas asked the SFX people to redo the scene so many times that they got annoyed and one of them threw in their shoe.
To preserve the dramatic opening of the Star Wars movies, George Lucas insisted on moving all the credits to the end of the film. However, although the Writers' Guild and Directors' Guild had begrudgingly allowed this on Star Wars: Episode IV - A New Hope (1977) (because that film wasn't expected to be very successful), they resented the trend being continued on this film. First they tried to pull Empire from release, but were unsuccessful. They then fined Lucas heavily, and tried to fine Irvin Kershner, but Lucas paid all the fines himself (nearly $250,000). Lucas then bitterly dropped his membership in the Writers' Guild, Directors' Guild, and the Motion Picture Association of America, a move that has hindered his hiring choices on later films (see also Star Wars: Episode VI - Return of the Jedi (1983) and Star Wars: Episode III - Revenge of the Sith (2005)).
Yoda's iconic manner of speech (i.e: "begun the war has" and things like this) has the parts of speech in Object Subject Verb order. Very few languages on Earth use this and most are based in the Amazon river basin.
Mark Hamill's wife gave birth to their first son (Nathan Hamill) early one morning, and Mark went straight from the hospital to shooting. This was the day they filmed the shots of Luke hanging by the weather vane below Cloud City, on Bespin.
There seems to be many stories behind Alec Guinness and his role as Obi-Wan Kenobi. In George Lucas's original treatment (When it was ALL one story instead of a trilogy), Obi-Wan lives throughout the whole story (A fact confirmed by Lucas in the DVD Commentary). However, Obi-Wan ends up getting killed off in the first film (Star Wars: Episode IV - A New Hope (1977), Episode IV: A New Hope). There are many stories as to why Lucas changed it. There are some stories that either Guinness demanded that Obi-Wan was killed off so he wouldn't have to appear in any sequels or Lucas did it on his own much to the bitterness of Guinness. In the Star Wars: Episode IV - A New Hope (1977), Episode IV: A New Hope DVD Commentary, Lucas says that he felt it was a waste of Guinness's talents to have him stand beside Leia in the control room during the Death Star battle (as it was scripted) and too outlandish to have the elderly Obi-Wan join the dogfight. So he killed off Obi-Wan in order to spur Luke on to going into Jedi training and defeat the Empire. In any event, when it came time to make Star Wars: Episode V - The Empire Strikes Back (1980), in which Luke begins his training, Lucas drew from the "ugly creature with mystical powers" mythological archetype (as he did when creating Star Wars) and created Yoda as Luke's new Jedi master. Eventually, Alec Guinness was lured back into the role of Obi-Wan when he was promised more money. Therefore creating the "force spirit" motif that remains throughout the rest of the films, including the new trilogy.
In the DVD commentary, Carrie Fisher relates that during some of the London filming, she stayed a house rented from Eric Idle. Idle and the Pythons were filming Life of Brian (1979) at the time. One evening, Idle had a small party, including Harrison Ford and The Rolling Stones, and served a potent liquor (which the Pythons had been distributing to extras on their film, to help boost morale) that he referred to as "Tunisian Table Cleaner". They stayed up most of the night drinking and having fun. The first scenes shot the next day were the arrival at Cloud City, which she says helps explain why she and Ford were so happy in those scenes. Idle is said to be pleased that he had a small hand in how the finished film turned out.
In the original script when Lando is about to lead Han, Leia, and Chewie into the trap set by Darth Vader, Lando offers his arm to Leia, as a gesture to lead her down the hallway and she accepts it. Harrison Ford ad-libbed Han coming up behind Leia and offering his arm to her at the exact same moment to imply that Han was jealous.
Before Star Wars had even been released, Mark Hamill was nearly killed in an automobile accident and as a result, had to have reconstructive surgery on his face. George Lucas used the Wampa attack to explain Luke's altered appearance. When Hamill asked Lucas what he would have done if Hamill had been killed in the accident, Lucas told him that he would not have recast the part of Luke. Instead, a new character would have been introduced that would be linked genetically, in some way, to Luke. This link would also explain the new character's strength in the Force.
For the 2004 DVDs, the scene with Darth Vader and the Emperor were redone replacing Clive Revill with Ian McDiarmid who played the Emperor in the rest of the series. The dialogue was re-recorded with Ian McDiarmid and James Earl Jones. Some additional dialogue was added.
One of the bounty hunters that Darth Vader hires to find Han Solo, IG-88, can be seen in the Cloud City. IG-88 is a droid, and his dead body is sitting next to a furnace in the room where C-3PO is dismantled.
When shooting on location in Norway, a fierce snow storm hit the hotel where cast and crew were staying. This would have normally halted filming, but director Irvin Kershner thought these weather conditions were an excellent opportunity to film the scene where Luke wanders through the snow after escaping the Wampa cave. He did this by sending Mark Hamill outside into the cold, while he and the cameraman stayed and filmed inside the hotel's front hall.
Another of the asteroids is actually a potato. It appears just as the Millennium Falcon first enters the field. Two asteroids travel from the top left to the bottom right corner of the screen. Just after the second asteroid leaves the screen a third one appears in the top left corner. This is the potato.
George Lucas was so impressed by Frank Oz's performance as Yoda that he spent thousands of dollars on an advertising campaign to try and get him an Oscar nomination for Best Supporting Actor. Lucas's campaign ultimately failed because it was felt that a puppeteer wasn't an actor.
In an interview with Cinescape magazine, director Irvin Kershner said that he thought the first film was trashy and how he had no interest in films with special effects. However, he was won over by George Lucas, although Kershner was determined to make the film more about characterizations than hardware. Kershner spent several months working on the script, pushing the writers into humanizing the characters more (something that Lucas has often been criticized for failing to do).
After an extra fell sick, Jeremy Bulloch (Boba Fett) was called in as a replacement to the Imperial Guard who escorts Princess Leia and pulls her into the elevator after she screams "Luke! It's a trap!". He's the same Imperial Guard who is captured by Lando Calrissian's men.
The entire Millennium Falcon was built live size for the first and only time for this installment (only half of the spacecraft was constructed for Star Wars: Episode IV - A New Hope (1977) and just part of it was used for the deleted sandstorm scene in Star Wars: Episode VI - Return of the Jedi (1983)). It measured 65 feet in diameter and 16 feet in height with a mandible giving it an overall length of 80 feet. The Falcon's weight was 23 tons.
The Millennium Falcon was constructed in a hangar at Pembroke Docks where great flying boats were made in the 1930s. It was brought to Elstree studios, London in sixteen interlocking sections by a convoy of trucks. After reassembly, the Falcon was floated into position on the then brand new Star Wars stage by means of compressed air pads similar to those used on hovercraft.
The entire sequence with the Wampa attack was designed to explain the difference in appearance of Mark Hamill, who had been in involved in a car accident in between shooting and had a large chunk of his nose missing. Noticeably, Kershner does not show much of Hamill's nose before the Wampa attack. The scene, however, was part of the story before Hamill's accident.
This movie featured the first appearance of the Emperor whom appeared as a hologram to Darth Vader. The 'Emperor' was actually portrayed by an elderly female stand-in with a hood and heavy makeup. The yellow, Dark-Force eyes were in fact chimpanzee eyes superimposed over the stand-in's eyes to give the Emperor a less-human, more unworldly look. The Emperor's voice was provided by Clive Revill who provided the voice only and not the appearance.
The Dagobah set needed to be elevated to give Frank Oz and three other puppeteers room to control the Yoda puppet from below. For proper interaction, Mark Hamill was given an earpiece so he could hear Oz doing Yoda's voice. On numerous occasions, Irvin Kershner would give a direction to Yoda by mistake and Oz would have to remind him who to talk to.
George Lucas had originally planned to only Executive Produce and finance the film, leaving the directorial duties in the hands of Irvin Kershner and day-to-day producing duties to Gary Kurtz. Directing the original Star Wars: Episode IV - A New Hope (1977) had left Lucas exhausted and sick, and he had intended to take time off to start to focus on the expansion of the Lucasfilm company and spending more time with his then-wife Marcia Lucas, that they could start a family and finish construction on Skywalker Ranch. However, when production on this film ran overbudget and behind schedule, Lucas had to step in and take a more hands-on role, going on location to oversee filming and even directing portions of the film. Lucas' absence put a horrible strain on his marriage and health, especially when a disastrous rough cut of the film proved incoherent during screenings. With his entire fortune invested in the film and facing the possibility of financial ruin, Lucas then re-edited the film himself with even worse results. Extensive reshoots and further post-production effects work put enormous strain on Lucas' health, his marriage, and his relationships with Kershner and Kurtz. Though the film proved an enormous critical and commercial success, Lucas would never work with Kurtz again, and his marriage dissolved several years later.
As Yoda and Obi-Wan urge Luke to stay on Dagobah to finish his training, Luke pulls a snake from his spaceship. Irvin Kershner assured Mark Hamill that the snake was harmless, though it did bite him during one take.
The bounty hunter dressed all in white is named Dengar. His backstory is that he was once a fierce rival of Han Solo's, and was badly beaten by him. He vowed revenge and has been hunting Solo for some time.
For the Special Edition, Vader's "Bring my shuttle" line has been replaced with, "Alert my Star Destroyer to prepare for my arrival." Sound designer Ben Burtt claimed this is actually a line performed by James Earl Jones that was recorded for use in Star Wars: Episode IV - A New Hope (1977), but never used; however, not only does the voice sound nothing like James Earl Jones, but the famous Imperial ships were NOT called Star Destroyers in the original film, but "star cruisers" -- even the novelization calls them such, so this one line would be an odd bit of discontinuity if Burtt's claims were true.
The AT-AT Imperial walkers were all animated through classic stop-motion techniques, except for the scenes where they fall, for example the walker which is "tripped up" by cables and falls on its face, or the one that Luke throws a grenade into, which falls on its side. These were filmed in real-time with precision-timed mini-pyrotechnic charges.
Boba Fett's action figure was originally to have had a rocket-firing mechanism, but after a child choked to death on a similar toy, Kenner dropped the mechanism and made the rocket stationary. A trace of the rocket launcher survived to the completed toy, however, as there is a rectangular area on the backpack in which the rocket launcher would have been embedded. The version with the mechanism is now considered the longest-running unobtainable action figure; contrary to popular belief, it was never sold to the public.
Han Solo's use of his mount's entrails to keep Luke warm is actually an American Indian trick. According to legend, an Indian hunter had killed a bear and then became trapped by a sudden blizzard. He cut open the bear's stomach and climbed inside and stayed warm and safe until the storm had subsided.
In the Star Wars galaxy, travel between the solar systems is via hyperspace routes; essentially, super-highways between stars. The route containing the planet Hoth is the equivalent of an unpaved road, which was why Admiral Ozzel was so skeptical that the rebels were there.
Features the only instance of breaking the fourth wall in the entire "Star Wars" saga. When several characters are escaping from the rebel base on Hoth as the Empire begins to invade, a door closes before C-3PO can exit through it, and he turns to the camera and mutters, "How typical."
The AT-ATs were inspired by the walking machines in H.G. Wells's "War of the Worlds" and their appearance was based on gantry cranes which are used in most shipping ports in the USA. Walking patterns of elephants were studied to make the movements seem as realistic as possible.
Dutch film director 'Paul Verhoeven' was considered to direct this film, based on his work in the film Soldier Of Orange. He was invited for a meeting with the producers and brought with him his newest film Spetters, that he was proud of and wanted to screen for the producers. After the screening he never heard from them again and the film would eventually be directed by Irvin Kershner. Verhoeven revealed this information at a Q&A session in Helsinki Finland during the Night Visions Film Festival in 2012.
The scene in the Cloud City apartment where Han Solo enters to tell Princess Leia that the repairs on the Millennium Falcon are almost complete played out differently in the finished film than it did in the original script. There, Han Solo (Harrison Ford) is lounging around in the apartment when Princess Leia (Carrie Fisher) enters, having changed from the white combat clothes she wore on Hoth to the brown dress and having her hair done up differently. In surprised reaction to how she's dressed, Solo attempts to flatter her ("You look beautiful. You should wear girls clothes all the time.") and Leia teases him by mentioning Luke; the scene ended with them sharing a kiss. The film was originally shot this way, but director Irvin Kershner felt it wasn't coming out right, so he re-shot it to appear as it does in the finished film. Excerpts of how the scene was originally filmed can now be seen on the special edition DVD.
The only Star Wars Original Trilogy film that does not take place on the desert planet Tatooine (although it is mentioned by name at the end of the film). Tatooine also appears in Episodes I, II, and III, making it the only planet that appears five times in the entire saga.
Harold Weed, an ILM staffer who assisted in designing the Wampa costume for the Special Edition, was cast as the Wampa for the film after he was used as the model for the costume. As he is 6 feet tall, the ice cave set for the re shoots was built with a height of 4 1/2 to 5 feet to create the illusion of the Wampa being closer to 8 or 9 feet in height.
In the Hoth command center, Han references "That bounty hunter we ran into on Ord Mandell". "Rebel Mission to Ord Mandell" was released in 1983 as an NPR radio drama, and later on 33 1/3 LP. It starred the voices of many of the original cast.
Harrison Ford was not expected to take part in the Norway leg of filming which represented the scenes based on the ice planet of Hoth, so his costume was built for the stage and consequently not very well insulated. At the last minute, weather conditions were such that the schedule needed to be changed, and it was decided to shoot his scenes in Norway instead.
The only way to get to the set in the midst of a blizzard during filming in Norway was on a snowplow train, which had a giant auger on the front, pushing through the snow to deliver the actors to the set. The weather conditions were so severe that the crew put the camera in the back door of the hotel the cast and crew were staying and shot from out the door, 12 feet from the hotel out in the blizzard.
Darth Vader's command module is said to be a hyperbaric chamber which charges the interior air to greater than one atmospheric pressure, thus allowing him to remove his helmet and breathe normally for limited periods of time; this was not as originally presented in the film, however, which featured an additional breathing mask for Vader in the chamber, which was notoriously shown for only a split second and never made it into the official continuity.
When escaping the asteroid field a tie fighter strikes an asteroid. As the asteroid travels down and to the right off screen, the pilot can be seen traveling down and to the left doing back flips as he travels off screen.
Most of the rebel ground troops in the Hoth battle were Norwegian extras. Because they didn't speak any English, second unit director Peter MacDonald had to "act out" what he wanted them to do, by pointing in the direction of the "enemy" (which wasn't visible during shooting) and demonstrating the recoil motion he wanted for the blaster rifles.
One of the first ideas for Lando Calrissian was to have him as a clone who survived the Clone Wars who leads legions of clones on a planet they settled on. Another idea had Lando as the descendant of survivors of the Clone Wars, born into a family who reproduced solely by cloning. Originally, his name was "Lando Kadar".
The swamp creature that tries to swallow R2D2 is never given a name in the film. It was eventually revealed, however, in the Super Star Wars: The Empire Strikes Back (1993) video game to be Hagobad (appropriately, an anagram of Dagobah, its home planet.)
Further scenes with the Wampa were shot, and later cut. R2-D2 encountered one within the Rebel base, where it was killed by troopers. Later, the beasts were lured into a prison within the complex. In the completed film, a medical droid is seen examining the wounds of a tauntaun killed by a Wampa, and Princess Leia mentions the "creatures" while discussing the Imperial probe droid. A scene filmed but cut had Han, Leia and C-3PO running through a corridor. Han went to take a short-cut through a door with a sign on it, but Leia warned him "that's where those creatures are kept". They run off, but not before C-3PO rips off the sign, hoping that the stormtroopers will enter the room. They did. A few seconds of this last scene can be seen in the theatrical trailer on the DVD.
About twenty minutes into the movie there is a shot in the Hoth base control room in which we hear Han's voice over radio describing what's left of the probe droid. One of the background sound effects in this shot was taken from the Canadian shortwave time signal station CHU, which can be heard at 3.330 and 7.335 MHz.
During principal photography it remained unclear if Sir Alec Guinness would return as Obi Wan Kenobi. Guinness was suffering from an eye infection at the time and was still a bit upset about the last minute decision of his character being killed off in Star Wars: Episode IV - A New Hope (1977). He finally did agree and worked one day on the film: Wednesday September 5 1979
The scenes where R2-D2 is submerged in the mud pool were shot in George Lucas' unfinished swimming pool. Most of the crew were hidden under the water and the entire sequence was shot by George Lucas himself.
The lightsaber fight scenes set in the carbon freezing chamber tend to focus on Luke. This is because during many of the shots, Bob Anderson (Vader's fight double) was not wearing the Darth Vader helmet, as it made it difficult for him to breathe.
George Lucas decided that a battle on an ice planet was necessary because he felt that it was easy to "cheat" in space, because the background was black and you could hide errors easily. With a white background, the effects crews would have to work much harder, and the effects would be much more impressive.
Director Harley Cokeliss, who was a friend of Frank Oz having worked with him on The Muppet Show (1976), visited the set towards the end of filming when the production team were struggling to get everything in the can before they ran over schedule. Cokeliss was hired on the spot as an additional director and is credited as one of the Second Unit Directors.
Irvin Kershner initially turned down the opportunity to direct the film as he felt that it would be too difficult to top the success of Star Wars: Episode IV - A New Hope (1977). He took the job when his agent convinced him that he shouldn't pass on the opportunity to make a sequel to one of the most popular movies in history.
A 1980 issue of the children's magazine National Geographic World featured an extensive behind the scenes look at the making of the film, and it's special effects. The issue included a popular pull out poster of a still photo image showing the Millenium Falcon being chased down by a Star Destroyer.
Originaly, the scene where Han rescues Luke on Hoth was to have been filmed at Elstree Studios, and only Mark Hamill was needed on location in Norway. But when a blizzard made it impossible to film anywhere but near the hotel, Harrison Ford was summoned to Finse, anyway. Unable to travel by train, he arrived in the engine compartment of a snow clearance vehicle.
The scene where Solo was hit by the toolbox as well as hitting the control panels were improvised on the set. At first, the crew were afraid of shooting it, but Irvin Kershner finally persuaded them to do so, saying "Come on, that's fun. Let's do it!"
The book "Star Wars: The Annotated Screenplays" reveals that, when the script for this movie was first written, the idea of it being "Episode V" of a 9 part serial had not yet been established, and it was at one point called Episode II.
Gary Kurtz was initially reluctant for George Lucas to hand over the reins to another director. It was only because Lucas trusted Irvin Kershner, his former teacher at USC, that Kurtz agreed to the move.
It has been widely rumored that Luke's injury early in the film was included to explain the difference in Mark Hamill's appearance, as a result of a car accident he had been in shortly after the release of the first film. In fact, however, that scene was already in the early drafts of the script before Hamill's accident.
Original start date of shooting at Elstree was slated to start in March 1979 but was delayed for three months because at that time, set 3 of the studio which was used for The Shining (1980) was burned down and had to be rebuilt at a higher scale
The two other scenes, which are the swamps of Dagobah; and the asteroid's creature (which has the Millenium Falcon) was done on the same sound stage used for the interior backgrounds of the Echo base in Hoth
A scene where Darth Vader's shuttle lands in his Star Destroyer's landing bay, after his light saber fight with Luke, was added to the Special Edition. This was actually an unused scene from Star Wars: Episode VI - Return of the Jedi (1983)
More scenes of the AT-ST Imperial "chicken walkers" were filmed, but George Lucas decided that the larger AT-ATs were more menacing and impressive. He later realized that the AT-STs would work better in close quarters, which led to using them extensively in the forest battle in Star Wars: Episode VI - Return of the Jedi (1983).
Darth Vader's costume was more detailed in this film, including the flashing red lights on his chest box. A new Millennium Falcon (32-inches long) was built for this film and has two additional landing gear boxes on its underside. As a result, the original Star Wars: Episode IV - A New Hope (1977) model (5-foot long) was modified and given the extra landing gear bays and was used for all FX scenes of the Falcon in a landed position.
The concept design for Cloud City was originally created for Star Wars: Episode IV - A New Hope (1977) (as a floating Imperial prison), but was never used. The design was recycled for use in this film.
Most of the extras in the snowy battle scenes on the ice planet Hoth (shot at Finse, Norway) were Norwegians. One of the extras - Tom Egeland - would later become the chief news editor for one of Norway's largest TV networks, as well as a critically acclaimed mystery writer, one of the others - Arve Juritzen - would become one of Norway's best known TV-personalities (hosting eg. Vil du bli millionær? (2000), Big Brother Norge (2001)).
Producer Gary Kurtz directed the scene in which Luke flees the Wampa ice cave. Kurtz took over John Barry's second unit duties after Barry suddenly died on the set, and until his replacement, Harley Cokeliss, arrived.
WILHELM SCREAM: Heard twice in the film. Once during the battle on Hoth as a rebel soldier and his laser gun dish explodes. And right before Han is going to frozen in the carbonite. As Chewie, in a fit if rage, throws a stormtrooper of the ledge (barely audible).
Yoda's appearance was originally designed by British makeup artist Stuart Freeborn, who based Yoda's face partly on his own and partly on Albert Einstein's, as his eyes are supposedly inspired by the latter. Yoda is voiced by Frank Oz. In the original Star Wars trilogy, he is realized as a puppet (controlled by Oz).
The chasm deep in the heart of Bespin in which Luke and Vader have their lightsaber duel was created using a matte painting. The same strategy was used in the original film in the scene where Luke and Leia blast Stormtroopers across an inactive bridge.
The armored speeders parked at the rebel base on Hoth were built by Ogle Design Ltd. of Letchworth Heath, near London. ODL is known for manufacturing the famous/infamous three-wheeled Reliant sports car.
Director Irvin Kershner decided that for this movie, members of the Rebel Alliance would speak with American accents, while the Imperial Officers would speak with British accents, to make the story analogous to the American Revolution. However, most of the supporting actors that appeared as Rebel personnel on Hoth were in-fact British actors. Consequently, Kershner had to re-dub several of the scenes taking place at the Hoth rebel base with American voices in post production.
The blizzard in the Hoth scenes is a real blizzard - no effects were used. Harrison Ford could not be gotten to the filming location via the regular train route as it was closed due to the bad weather - so he had to be gotten to the site on a snow plow.
The trivia items below may give away important plot points.
Security surrounding this movie was so intense that George Lucas had regular reports about "leaks" from actors. George Lucas was so determined that the ending be kept secret that he had David Prowse (Darth Vader) say "Obi-Wan killed your father", and dubbed it later to be "I am your father". In fact, only five people eventually knew about the ending before the film's release: George Lucas (came up with the idea in his second draft, after the death of Leigh Brackett), director Irvin Kershner (informed of such during story conferences), writer Lawrence Kasdan (also informed during story and script conferences), Mark Hamill (informed shortly before the shooting of the infamous scene), and James Earl Jones (told during the recording sessions for the final dub, and whom himself believed that Vader was lying).
During his battle with Vader, Luke's hand is severed and he loses his lightsaber (once used by Anakin/Vader and given to Luke by Obi-Wan). As part of the Expanded Universe, Luke's hand and lightsaber were recovered and kept by the Emperor as trophies. Later, the hand was used to create a clone of Luke that also wielded the lost saber. After the clone's death, Luke presented the lightsaber to Mara Jade, his future wife.
When Luke and Han say their goodbyes before the Battle of Hoth, it is the last time Harrison Ford and Mark Hamill are on screen together until they meet up in Jabba the Hutt's palace in Star Wars: Episode VI - Return of the Jedi (1983). There is one scene in Cloud City wherein Hamill shares a scene with a "carbonized" mannequin of Ford.
In Leigh Brackett's original draft of the script, Darth Vader was not Luke's father. The character of Anakin Skywalker actually appeared in the film as a Force ghost to train Luke. Anakin's characterization was later split into the characters of Yoda, and to allow Obi-Wan Kenobi to appear in the film.
Leigh Brackett's first draft of the screenplay contained the revelation of Luke's sister, her existence disclosed by the ghost of Anakin Skywalker. Referred to as "Nellith Skywalker", Anakin explains that it was he, not Obi-Wan, who separated the twins at birth to protect them from Darth Vader, and that Nellith also underwent Jedi training in another part of the galaxy so she could join forces with Luke to defeat the Sith. This concept was dropped in the second draft of the screenplay, along with the appearance of Anakin Skywalker and replaced with a scene of Obi-Wan and Yoda discussing how they must find another Jedi apprentice in anticipation of Luke's failure. This too changed in later drafts, resulting in the more ambiguous scene in the final version where Yoda assures Obi-Wan that "another" exists.