The Jedi of The Empire Strikes Back.
The Jedi Order has been a Star Wars mainstay since 1977, as has the mysterious powers they employ through the Force. The Force was initially described as an energy that binds the universe together and has since been shown to allow Jedi to manipulate the minds of the weak, move objects through telekinetic means, and connect with creatures of the galaxy in several ways. While these are only a select few of the many powers the Force provides, one allows the Jedi to extend their life beyond death.
This ability was explored in detail in Force ghosts in canon, many Jedi have appeared as such across the Star Wars timeline, and here is a comprehensive list of every character in question.
Obi-Wan Kenobi
The first appearance of a Force ghost in Star Wars, at least in of release order and not chronologically, was Obi-Wan Kenobi. At the beginning of The Empire Strikes Back, after Luke escapes the Wampa's cave, he is stranded on Hoth in a blizzard. During his weak state, Luke sees Obi-Wan as a Force ghost, with his old master encouraging Luke to seek out Yoda on Dagobah to continue his Jedi training. Over the remainder of The Empire Strikes Back and Return of the Jedi, Obi-Wan continues to appear as a Star Wars: The Force Awakens despite not appearing physically.
Yoda
Yoda is the next character, again in release order, to appear as a Force ghost after Obi-Wan Kenobi in the final scene of Return of the Jedi. Like Obi-Wan, Yoda simply faded upon his death leaving behind no physical body, leading to his appearance as a Force ghost after Luke defeats the Emperor and sees the downfall of the Galactic Empire. Yoda's journey to learning this ability is shown in the final arc of The Clone Wars season 6 before he is shown as a Force ghost in Return of the Jedi and later in Star Wars: The Last Jedi alongside an older Luke Skywalker.
Anakin Skywalker
Return of the Jedi saw Force ghost Anakin appear in the final scene of the film alongside both Yoda and Obi-Wan Kenobi. Initially, Anakin's Force ghost was portrayed by Sebastian Shaw, before being replaced in the original trilogy special editions by Hayden Christensen's version of Anakin from the prequel trilogy. Despite the change, Anakin as a character remains another canon Jedi to appear as a Force ghost. While many wondered how Anakin can do this, due to him likely not receiving the same training as Yoda and Obi-Wan, Anakin's status as the Chosen One is often theorized as the reason why he can continue on after death. Also, George Lucas has cited Anakin's redemption and return to the light as explanations for his Force ghost ability.
Qui-Gon Jinn
Qui-Gon Jinn, Obi-Wan Kenobi's old master and former padawan of Count Dooku, was first shown as a Force ghost in Star Wars: The Clone Wars on Mortis. In the show, Mortis was established as a conduit through which the entire Force in the universe flows which allowed Qui-Gon Jinn to physically appear as a Force ghost to Obi-Wan. While Qui-Gon had been through the same training shown in Yoda's Clone Wars arc, he died before being able to finish his training. However, it is theorized that this wasn't the case, as Obi-Wan Kenobi shows Qui-Gon appearing as a Force ghost before Obi-Wan on Tatooine during the time of the Galactic Empire.
Luke Skywalker
Hero of the original trilogy Luke Skywalker has also appeared as a Force ghost, shown in the final installment in the Skywalker Saga: Luke's death at the end of Star Wars: The Last Jedi, he instead becomes one with the Force like his old masters Obi-Wan and Yoda, leaving no physical trace behind. This set up Luke's Force ghost appearance in Episode IX, in which Luke appears to Rey on Ahch-To. Luke's Force ghost talks Rey out of her crisis and convinces her to fight on for the Resistance, before appearing at the end of the film in the skies of Tatooine alongside Star Wars canon's final Force ghost appearance...
Leia Organa
Star Wars: The Rise of Skywalker's final sequence includes two Force ghosts in the Skywalker twins. After Rey buries Luke and Leia's lightsabers at the Lars' homestead on Tatooine, she looks to the sky to see both Luke and Leia as Force ghosts, inspiring her to take on the name of Rey Skywalker. Like Anakin, it is unclear how both Luke and Leia became one with the Force and appeared as Force ghosts. However, given the two are the children of the Chosen One, Anakin's power over the Force could transfer to them allowing the Force ghost abilities the twins possess.
The Rise Of Skywalker Jedi Voices
While The Rise of Skywalker only features two physical Force ghosts, Luke Skywalker and Leia Organa, one of the film's climactic scenes features many Force spirits communicating with Rey. Again, these characters don't feature physically meaning they aren't technically Force ghosts like the other characters on the list. However, the many Jedi voice cameos in Rise of Skywalker coming to Rey in her moment of need certainly count as Force spirit powers, as most (if not all) of the characters are dead at that point in the timeline. These characters include Ahsoka Tano, Kanan Jarrus, Luminara Unduli, Aayla Secura, Mace Windu, and Adi Gallia. While those mentioned have never appeared physically as a Force ghost, their Force connection with Rey can surely be classed as a Force ghost appearance in Star Wars canon.
