During the Imperial Era, sometime following the events of the Duel on Cloud City, Darth Vader, the Sith Lord, embarked on a quest. This journey led him to the planet Exegol, situated within the Unknown Regions of the galaxy. His purpose was to face his Sith Master, Darth Sidious, the Galactic Emperor also known as Sheev Palpatine, the Dark Lord of the Sith, and to learn the truth behind his power.
After his lightsaber duel on Cloud City with Luke Skywalker, his son and Jedi apprentice, Darth Vader became determined to find out how his son had survived the death of his wife, Padmé Amidala, years prior. He disobeyed the orders of his Sith Master, Darth Sidious, the Emperor of the Galactic Empire, and began his own search for answers. On Naboo, the homeworld of his late wife, Vader eventually discovered the Amidalans, a resistance group that mistakenly believed Vader was responsible for Amidala's murder, unaware that he was actually the former Jedi Knight Anakin Skywalker. Through the Amidalans, Vader witnessed the demise of his pregnant wife on Polis Massa via an ancient holographic recording, and only then did he return to his master.
As punishment for his insubordination, the Emperor decided to teach Vader a lesson about the dark side of the Force. He removed Vader's cybernetic limbs and had him abandoned on Mustafar by a squad of death troopers, intending to either strengthen his Sith apprentice through suffering or leave him to die. The Emperor also sent Ochi of Bestoon, a Sith assassin, to hunt Vader down, and dispatched Sly Moore, an Umbaran Administrator and aide, to oversee the operation. Vader managed to temporarily repair his suit using makeshift components. The Dark Lord eventually located the Eye of Webbish Bog, the guardian of a Sith wayfinder, and obtained the wayfinder after the creature tested him using the Force.
Vader apprehended Ochi and repaired his former Eta-2 Actis-class light interceptor, using it to journey to the coordinates indicated by the wayfinder. This led him to Exegol, a planet situated in the unpredictable Unknown Regions of the galaxy, accessible only by navigating the Red Honeycomb Zone within the Galactic Barrier. Moore, along with an Imperial fleet under the command of Admiral Corleque, attempted to pursue Vader, but they were forced to abandon the chase when the Sith Lord entered the nebula and encountered a subspecies of the summa-verminoth. Vader successfully traversed the Red Honeycomb Zone and landed on Exegol's surface with Ochi.
From a high vantage point, Darth Vader observed his master, Sidious, positioned just beyond the Sith Citadel, declaring that he was no longer the Emperor's apprentice. Ochi rushed to the Emperor, warning his lord of Vader's approach, but Palpatine dismissed the warning, stating that he had anticipated Vader's arrival. Using the Force, Vader summoned the summa-verminoth from the Red Honeycomb Zone to attack the Emperor, killing two crustacean beasts used by the Emperor, but the Sith Lord killed the creature with the Force, knocking down the cliff and Vader in the process. Sidious then retreated into the Sith Citadel, pursued by Vader and Ochi.
Within the subterranean fortress, Vader stumbled upon a laboratory containing numerous genetic strandcasts stored in vats while chasing his master, who explained that he had used "pain" as a "scalpel of creation" while Vader looked on the severed hand of his son, Luke Skywalker. Four armored strandcasts known Tankers, armed with electropoles, were released from their vats and attacked Vader as the Emperor proclaimed that any of them could take Vader's place as a Sith. Vader eliminated all four guardsmen, but during the battle, the ground beneath them collapsed, causing Vader to fall deeper underground. There, he encountered a group of Sith cultists armed with daggers. As the cultists attacked Vader, Palpatine claimed they could also replace Vader as one of the two Lords of the Sith. However, Vader used the Force to seize the cultists' daggers, hurling them back at the group and killing them.
Vader continued to pursue the Emperor as Ochi continued to proclaim that his apprentice was still coming for him, but Sidious mocked Vader's desire for vengeance. Drawn deeper beneath the temple by an overwhelming sense of pain, Vader discovered the construction site where a vast reserve of Star Destroyers equipped with planet-destroying cannons was being built. Vader was then drawn to a structure containing a massive kyber crystal, while Ochi tried to convince him to reason with the Emperor. As more Sith cultists drilled into the kyber crystal, causing it intense suffering, it unleashed a powerful burst of fire and wailing, sending the cultists flying back and blinding Ochi.
Sidious informed Vader that he could only share his power through experiencing pain, and presented him with a choice. Despite being weakened and injured, Vader ultimately chose to remain by the Emperor's side. Although he had a vision of Skywalker telling him he was destined to destroy Sidious, Vader had witnessed the immense power he possessed over him, convincing the Sith Lord to return to his master's service because of that power. The Emperor and Vader then departed Exegol, accompanied by Ochi, Mas Amedda, and Sly Moore.
Following his mission to Exegol, Darth Vader was returned to Coruscant, the Imperial capital, where he underwent the reconstruction of his cybernetic armor in the secret laboratories of the throneworld.
Vader remained loyal to the Emperor in the year that followed, feeling compelled to serve his master due to the power of the dark side of the Force. During the Battle of Endor, Vader brought his son, Luke Skywalker, before the Emperor in his throne room aboard the second Death Star, where the Emperor sought to convert Skywalker, the last of the Jedi, to the dark side. However, Vader's inherent goodness was rekindled by his son's compassion and love, as Skywalker regained his composure and refused to kill his father, discarding his lightsaber. The Emperor attempted to kill Skywalker, but Anakin intervened, sacrificing himself to save his son by destroying the Emperor. The redeemed Anakin died in his son's arms shortly after, having vanquished the Sith and brought balance to the Force.
Approximately three decades later, during the First Order-Resistance War, Kylo Ren, the Supreme Leader of the First Order and grandson of Anakin Skywalker, sought to locate the source of a mysterious broadcast using the late Emperor's voice, viewing it as a challenge and a threat to his authority, and eliminate it. Guided by the esoteric Sith religion lore he had discovered from the bases of his predecessor and former master, Snoke, Ren was drawn to Mustafar in search of artifacts that could aid him in his quest.
During his mission to Mustafar, Ren recovered his grandfather's Sith wayfinder from the Eye of the Webbish Bog, which guided him through the Unknown Regions to Exegol, the fabled hidden world of the Sith. There, Ren encountered a resurrected Darth Sidious, reborn in a clone body following his demise at the hands of the redeemed Anakin Skywalker, along with his followers, the Sith Eternal, and their Contingency military force, the Final Order. Ren learned that Sidious and his disciples had groomed him as the heir to a new Sith Empire poised to be unleashed from Exegol and to inherit the legacy of the Sith; as well as that his master, Snoke, had been a genetic strandcast and proxy created by the resurrected Dark Lord and his followers.
However, Ren ultimately rejected the dark side when his mother, General Leia Skywalker Organa Solo of the Resistance, sacrificed herself to reach out to him and reaffirm her love and forgiveness, and when he subsequently experienced a vision of his father, Han Solo, whom he had murdered, forgiving him. The Supreme Leader reclaimed his birth identity as Ben Solo and joined forces with Rey, the Emperor's granddaughter and the Jedi apprentice of Luke and Leia Skywalker, in confronting the last Sith Lord. Empowered by the spirits of the Jedi past, Rey defended herself against the Emperor, ultimately vanquishing him and his followers, preventing the resurgence of the Sith and the restoration of the Empire.
Though Rey died in the process, Solo gave his life force to resurrect her, made possible by their being a dyad in the Force, making a sacrifice that recalled that of his grandfather. Redeemed by this selfless act, Solo passed away into the Force, joining with his mother. Rey went on to repudiate the Palpatine name, and declared herself Rey Skywalker as the spirits of Luke and Leia watched on approvingly, honoring her mentors and continuing the Skywalker family legacy. Rey went on to become a Jedi Master herself as she fought to restore galactic peace.