Force ghost

"What is a Force ghost?''" "''It's a survival, a sending from someone who has died but still exists in a certain way."

- Ordith Huarr and Nelani Dinn

The Force ghost was the soul and essence of a deceased Force-sensitive who denied the will of the Force upon death, yet was able to interact with the living, albeit not physically. Some Sith Lords learned similar techniques, which in some cases allowed them to physically interact with their environment.

Description
"I was able to touch you because we are connected by the Force. I drew on your link with the Force to become more solid, just as I draw on it now to become visible to you."

- The ghost of Aidan Bok to Tash Arranda

While most Jedi would lose their bodily envelope and become one with the totality of the Force upon their death, some had learned a technique allowing them to retain their own identities separate from the Force for a time. Those individuals could linger in the physical world in the form of "Force Spirits," nonphysical entities that exhibited most traits and abilities they had in life. According to the knowledge contained in Asli Krimsan's holocron, that feat could be achieved by sublimating one's organic cells into a state of pure energy.

In its "normal" state, a Force Spirit could only interact with other noncorporeal entities. In order to be heard or seen by the living, the Spirit had to manifest itself. There were different types of manifestation. On a basic level, a Force ghost could appear as a floating, milky gray mass of energy that lacked distinctive features. But it could also manifest itself as the exact image of the dead being during their lifetime, only transparent and emitting a bluish glow. While it could appear to anyone it wished, a spirit could not choose to become audible or visible to only some beings and not the others, since the ability to perceive the manifestation depended on the beholder's strength in the Force. While many Force ghosts could appear as a vision of their former selves unmarked by injury or disease, others still bore the marks of what killed them. The ghost of Aidan Bok wore tattered robes and had gaping wounds in its body, the marks left by a lightsaber. Sometimes, a particular Force ghost would bind itself to a Force-sensitive as a guardian spirit for the purpose of providing wisdom, continuing training, and offering aid.

In theory, Force spirits could neither harm or be harmed by physical entities, due to their spiritual nature. For the same reason, they could pass through solid matter effortlessly and were never hampered in their movements. While some spirits would simulate the walk of the living beings, subject to gravity, others would hover and drift above ground level. However, in some cases, a spirit could acquire temporary solidity by drawing on a living creature's link with the Force, which allowed it to actually touch that creature. Notably, the ghost of Aidan Bok could make itself solid enough to shove Tash Arranda through a doorway.

A manifested spirit could wield Force powers, although not all of them. It also had the ability to travel instantaneously to any point in the galaxy by force of will. That power, however, required that the spirit be familiar with the destination. The presence of the Force at the place of arrival was also necessary for that ability to work, since it acted as a beacon.

History
"Eternal life&hellip;''" "''The ultimate goal of the Sith, yet they can never achieve it; it comes only through the release of self, not the exaltation of self. It comes through compassion, not greed. Love is the answer to the darkness."

- Yoda and Qui-Gon Jinn

According to the Jedi tradition, death was a part of life, and it meant becoming one with the Force. In death, sentients lost their ability to communicate with the living, but mastery of certain obscure paths of learning could avert it.

The origins of that knowledge, as well as its history, are not known. Ancient Jedi of the Galactic Republic such as Arca Jeth, as well as Sith Lords, knew a secret which could enable the user's essence to "survive death", but this knowledge was somehow lost over the millennia. However, it was secretly preserved over the millennia by the native Ysanna, descendants of Jedi trapped on the world and slowly driven to barbarism.

Rediscovery
Qui-Gon Jinn was the first of the recent Jedi who rediscovered this secret with the assistance of a shaman of the Whills. Qui-Gon's spirit guided Yoda (Leading him to meet the five priestess) and Obi-Wan Kenobi and revealed to them the secret of retaining one's individuality after becoming one with the Force. Yoda during his exile taught it to another Jedi Master, Qu Rahn. The Dark Woman also learned of it at some point.

Death for those Jedi were different: their spirits could retain their individuality and could return as voices, dreams, or apparitions at will, so that they could help those in need of their guidance. On death, their bodies vanished; this was not the case with Qui-Gon, however. This state was temporary, as Force ghosts were an intermediate state between life and afterlife; after a certain amount of time, they would then have to move on to the Netherworld of the Force, another realm of existence. Darth Vader learned of this ability through Darth Sidious, and upon his death, the spirits of Kenobi and Yoda completed his training by granting him the last step in becoming a spirit. Anakin's spirit appeared as that of his younger self, prior to his fall to the dark side.

Similar techniques
Certain Sith Lords had also discovered similar techniques. Occasionally their bodies would fade as Jedi would, though like Jedi this was not a prerequisite for becoming a Force ghost. It was not uncommon for the spirits of Sith Lords to remain, bound to the living world through an object, location, or simply due to the force of their malice and hatred. Unlike the Jedi, however, the Sith found little peace in this form, instead existing for restless centuries, eventually driven insane by solitude, memories, or dark side inflicted madness. In many ways, these techniques differed from those taught by the Jedi; the most distinct difference being the user's limited ability to interact with his surroundings. One proficient Sith user of these techniques was Exar Kun.

Notable Sith such as Darth Andeddu and Darth Bane feared their own mortality rather than embracing it and becoming ghosts of the Force such as their Jedi counterparts. Due to this fact they sought ways to escape death and live on indefinitely. Though there was much speculation, Bane's body did not disappear and become one with the Force when he died. His soul was absorbed into his apprentice's body and dominated by her soul leaving behind only a trace of his soul. In this case and many others the Sith lived on only in the small essences of their souls that they embedded into their Sith holocron's. Where as the many Jedi who believed that there was no death only the Force lived on forever through the acceptance of their death. The Sith believed that the Force would free them and break their chains that bound them to their mortal coil.

Known Force ghosts
A † indicates that although their body did not vanish, they later appeared as a ghost. A # indicates that the individual's body exploded upon death and may continue existence in a spirit form.''
 * ''A * indicates that the individual had no known ghost appearances (so far). However, their body vanished upon death which implies that they may have known this technique.

Jedi

 * Jesper Altax
 * Aryzah
 * Vodo-Siosk Baas
 * Empatojayos Brand
 * Daeshara'cor *
 * Orgus Din †
 * Dominus *
 * Nejaa Halcyon *
 * Noab Hulis
 * Ikrit
 * Arca Jeth *
 * Qui-Gon Jinn †
 * An'ya Kuro
 * Last Curator of Records *
 * Kento Marek †
 * Crian Maru
 * Callista Ming
 * Celeste Morne
 * Obi-Wan Kenobi
 * Odan-Urr *
 * Ooroo *
 * Pernicar
 * Lanius Qel-Bertuk
 * Ulic Qel-Droma
 * Qu Rahn
 * Rajivari
 * Wolf Sazen *
 * Echuu Shen-Jon
 * Anakin Skywalker
 * Kol Skywalker †
 * Luke Skywalker
 * Mara Jade Skywalker
 * Anakin Solo †
 * Jacen Solo
 * Andur Sunrider †
 * Meetra Surik
 * Tahl
 * Tal
 * Shaak Ti #
 * Matta Tremayne *
 * Hosk Trey'lis
 * Kazdan Paratus *
 * Dree Vandap
 * Halagad Ventor
 * Vergere (Was also trained as a Sith)
 * Celeste Morne *
 * Yoda
 * Revan
 * Jem Ysanna *
 * Nerra Ziveri
 * Lyoon

Dark Jedi

 * Joruus C'baoth #
 * Jerec *
 * Kueller (appears in dream)

Sith

 * Tulak Hord
 * Darth Andeddu †
 * Darth Andru
 * Darth Bane
 * Darth Caedus †
 * Darsin
 * Ergast
 * Quorlac Fornayh
 * Githany
 * Horak-mul
 * Dathka Graush †
 * Darth Iratus
 * Skere Kaan
 * Aloysius Kallig
 * Exar Kun †
 * Darth Krayt
 * LaTor
 * Saalo Morn
 * Terrak Morrhage
 * Karness Muur †
 * Freedon Nadd †
 * Darth Nihilus *
 * Ajunta Pall
 * Darth Sidious #
 * Qordis †
 * Marka Ragnos †
 * Naga Sadow
 * Darth Vectivus
 * XoXaan †
 * Darth Zash
 * Kalatosh Zavros

Other

 * Denin
 * Zeth Durron
 * Father *
 * Tag Greenley (non-canon)
 * Grotrugga
 * Dice Ibegon
 * Herian I'ngre
 * Morgan Katarn †
 * Kimania
 * Dllr Nep
 * Neas Nyl
 * Teril Nyl
 * Bink Otauna (non-canon)
 * R5-D4 (non-canon)
 * Risstenni
 * Lak Sivrak
 * Vila
 * Erpham Warrick
 * Zik'tath

Behind the scenes
"Luminous beings are we, not this crude matter."

- Yoda to Luke Skywalker

Retcon
During the original trilogy, fans and Expanded Universe writers believed that this happened to all Jedi who died, even fallen Jedi who repented at the end of their lives, such as Darth Vader and the Jedi Ulic Qel-Droma. In the latter case, the vanishing was a sign that his spirit was redeemed. In works such as Tales of the Jedi, most Jedi who die are seen dissolving, and sometimes later appearing as ghosts.

Many questions arose during The Phantom Menace, when Qui-Gon Jinn's body did not vanish after his duel with Darth Maul, and instead was cremated on a Jedi funeral pyre like Vader. In Revenge of the Sith it is made known that "dying AND maintaining one's identity" is not in fact what happens to every Jedi, but an ability acquired by Qui-Gon's spirit and passed on to Yoda and Obi Wan.

On the other hand, Qui-Gon Jinn was the first character to show Star Wars audiences that not all Jedi became Force ghosts upon dying (by virtue of his body not disappearing at death), but he was established in Attack of the Clones as a voice to Anakin Skywalker, and also in Revenge of the Sith as the first G-canon character to learn how to become a Force ghost, despite his body not disappearing at death. The implication is that one can learn how to be a Force ghost even after dying a standard death. Mara Jade Skywalker did something similar after dying. She only faded away when Jacen (secretly Darth Caedus) entered the room in a last ditch effort to inform the Jedi about him, which would seem to imply that a Force-user who has mastered the ability to turn into a Force ghost has control of their body.

Anakin Skywalker
It is explicitly stated in Champions of the Force and the Databank on the official site that the organic part of Anakin's body disappeared, and that Luke just burned his suit and mechanical parts for ritualistic purposes.

Controversy sparked when, in the DVD of Return of the Jedi, Sebastian Shaw's Force ghost was replaced by that of Hayden Christensen's image, thus removing Shaw's Force ghost from canon and placing Christensen's in its stead.

Other problems
Another problem that remains to be retconned is the existence of spirits of Sith and Dark Jedi. In both the novel and the comic book version of Revenge of the Sith, the spirit of Qui-Gon Jinn tells Yoda that only light-siders may live on as Force ghosts, and that this is something that dark-siders cannot learn. However, in Dark Lord: The Rise of Darth Vader, Darth Sidious (who mastered and perfected the technique with the use of clone bodies himself) reveals that the ancient Sith Lords once had the ability to "survive death", but this knowledge was somehow lost over time. It is unclear which Sith Lords qualify as "ancient" in this context, although Skere Kaan and Qordis were the last known Sith to have escaped being lost in the Netherworld of the Force before Palpatine. It could be possible that Qui-Gon was misinformed or rather the concept of it only applying to Light side users was simply one of his many (often radical) theories. There is also the distinct possibility that light side Force ghosts and dark side Force ghosts are fundamentally different, and that's what Qui-Gon meant. Indeed Jedi Force ghosts seem to be "freed" into the netherworld by the passing of their physical forms and conversely, Sith Force ghosts seem to be "trapped" or attached by death, be it to a relic (the Muur Talisman, Ulic Qel-Droma's Sith amulet, etc.) or to specific locations (such as the Massassi Temples in Yavin IV, ancient Sith tombs, etc.). This however has yet to be confirmed.

This question applies to non-Jedi, such as Morgan Katarn who have appeared in that form. It is assumed that spirits of Force-sensitives, although not fully trained Jedi when they lived, can be manifested by the Force in a Force nexus (places where it is extremely strong), such as the Valley of the Jedi. Also, the Sith Lord Ajunta Pall lived on through the Force in such a manner as a Force ghost, though it is relatively unknown how or why he remained. However, it can be speculated that his extreme rage and anger made his presence linger. This has been applied to Exar Kun, who used the dark side to feed off of the life force of the Massassi just before he died. It may be possible that spirits of other Sith Lords latched onto a place strong in the dark side, feeding off of it like a parasite. The process may be explained in a future novel or other source.

Non-canon
The non-canonical characters Tag Greenley and Bink Otauna become Force-ghosts after dying in the explosion of the second Death Star, and appeared on Endor next to Obi-Wan, Yoda, and both a younger and older vision of Anakin Skywalker.

Mace Windu appears as a Force ghost in the alternate history comic Star Wars Infinities: The Empire Strikes Back in a vision to Darth Vader, though this may only be a mental vision in Vader's mind as opposed to an actual Force ghost.

The Force ghost versions of Anakin Skywalker, Yoda, and Ben Kenobi are playable characters on LEGO Star Wars II: The Original Trilogy and LEGO Star Wars: The Complete Saga.

In the Star Wars Tales story Skippy the Jedi Droid, the title character (otherwise known as R5-D4) becomes a Force ghost following his destruction by the Empire.

In the Robot Chicken: Star Wars special, Jar Jar Binks is turned into a Force ghost after Darth Vader ejects him from an airlock.

The Force Unleashed Ultimate Sith Edition depicts that Obi-Wan's Force ghost is able to be affected by Starkiller's Force attacks, including Force lightning.

Non-canonical appearances

 * The Force Unleashed Ultimate Sith Edition
 * Star Wars Infinities: A New Hope
 * Star Wars Infinities: Return of the Jedi
 * LEGO Star Wars II: The Original Trilogy
 * LEGO Star Wars: The Complete Saga