The search for Exegol was an effort carried out by Supreme Leader Kylo Ren of the First Order in 35 ABY to cement his control over much of the galaxy. His quest was launched in response to a mysterious broadcast that threatened revenge in the voice of the long-dead Galactic Emperor Sheev Palpatine, the Sith Lord Darth Sidious. In secret, Sidious's spirit had circumvented death by inhabiting a clone body on the planet Exegol in the Unknown Regions, where he was attended to by a hidden cult of Sith loyalists.
Kylo Ren became Supreme Leader of the First Order after killing Snoke.
In 35 ABY, a mysterious broadcast was transmitted across the galaxy that used the voice of the deceased Emperor Palpatine, secretly the Sith Lord Darth Sidious, to make a threat of revenge. This was perceived as a challenge to Supreme Leader Kylo Ren's authority, who himself saw its source as a threat to his newly obtained power. Ren was determined to eliminate any threat to his power, and, as such, immediately refocused First Order efforts from the ongoing First Order-Resistance War to finding the source of the broadcast and eliminating it. What Ren and even the highest echelons of the First Order did not know was that the Dark Lord had been secretly resurrected in a clone body on Exegol. There, deep in the impenetrable Unknown Regions, the deposed Emperor remained in exile, attended to by a cult of Sith loyalists that carried on the Sith tradition and sought to fulfill the former Emperor's plans to usher in a new Sith Empire.
Supreme Leader Ren led the First Order to Mustafar in his search for Exegol.
As he consolidated his hold over the First Order, Ren uncovered the bases of his predecessor Snoke, and realized that even the former Supreme Leader had been subservient to some greater power. Guided by the teachings of his former master, Ren focused himself on the search, raging in search of answers to ensure he would bow to no one. Ren's efforts ultimately led him to the Outer Rim world of Mustafar, the former home of his grandfather, Sith Lord Darth Vader. Leading a squad of stormtroopers, Ren and his troopers fought against the Alazmec of Winsit, a Sith cult from the Corvax Fen plain that worshiped Vader, in order to reach the ruins of Fortress Vader. Outpacing his stormtroopers, Ren arrived at the ruins and met the Eye of Webbish Bog, who gifted him Vader's wayfinder.
Sidious entreated Ren to succeed where Vader failed, destroying the last Jedi and becoming the new Emperor.
With the name "Exegol" suddenly within his mind, Ren followed the wayfinder to Exegol to confront Sidious and find the power he knew would be hiding on the planet. There, Ren uncovered the Sith Eternal cult and met the phantom Emperor, learning of his continued existence. The Emperor offered Ren command of the Sith Eternal's fleet, the Final Order, if he killed the Jedi apprentice Rey, whom he revealed to Ren to be his granddaughter. Ren agreed, realizing that he had been groomed as heir to the new Sith Empire waiting to be unleashed from the depths of the Unknown Regions. However, the young Supreme Leader had no intention of serving the Sith, feeling that he had sacrificed far too much to be subservient again. Instead, Ren sought to ally with Rey so that they could kill the former Emperor and rule the galaxy together.
The First Order and Sith Eternal became uneasy wartime allies.
Supreme Leader Ren was suspicious of Sidious' motives, but believed that, by combining his forces with those of the Sith Eternal, the First Order would become a true Empire with himself as its Emperor. The Supreme Council initially found itself at odds with their Supreme Leader's reactive nature and complete submission to the dark side, as the orthodox First Order officers preferred more traditional military tactics for their conquest of the galaxy. Upon Ren's return to the First Order, General Domaric Quinn expressed skepticism of the cult, referring to them as conjurers and soothsayers.
However, Allegiant General Enric Pryde noted that an alliance with the cult would increase their military assets ten-thousandfold, bolstering their forces to the might of that of the former Galactic Empire. Unknown to all, Pryde was an agent of the Sith Eternal and served the reborn Sidious above all. Ren's promise of new warships and soldiers from the Unknown Regions bolstered the Supreme Council's confidence in him, and they ultimately supported his alliance with the Sith Eternal. As a result, the First Order began to ready the elite army in their ultimate push towards galactic conquest. Even so, however, a simmering tension brewed between the well-regimented military of the First Order and the mystical cultists of the Sith Eternal.
The First Order and the Sith Eternal were ultimately defeated at the Battle of Exegol.
After Ren renounced the First Order and the dark side, the Sith Lord contacted General Pryde, a veteran of the Empire, and summoned him to Exegol to collect the Sith fleet. As the Sith Eternal prepared their fleet for launch into hyperspace, the Resistance invaded the Sith redoubt at the Battle of Exegol to stop the fleet before it could deploy across the galaxy and augment the First Order's forces. The Sith fleet was ultimately smashed after the Resistance was reinforced by a rallied fleet of civilians during the battle at Exegol. Their victory inspired a popular uprising against the First Order, and the First Order fell across the galaxy as its military rule crumbled without their Sith reinforcements. The Emperor and his followers were killed by Rey when she sacrificed herself to embody the spirits of the Jedi past, though Rey was healed back to life by Ben Solo, who gave his life for hers.
- Star Wars: The Rise of Skywalker: The Visual Dictionary
- "A Certain Point of View" — Star Wars Insider 213