Return of the Jedi ended with the death of Palpatine, but his defeat also created a power vacuum that other powerful dark side users would try to fill in both canon and the original Star Wars timeline, Legends (formerly called the Expanded Universe). Although Darth Bane’s Sith Order was destroyed, dark side practitioners and new forms of the Sith Order would return. Along with the remnants of the Empire itself, these villains would continue to plague the galaxy at large and the heroes of the original trilogy for the following decades as the New Republic and New Jedi Order were established.
In canon, there are few dark side users outside of the First Order’s leadership and the Knights of Ren. Palpatine ensured the survival of both the Empire and his Sith legacy through a series of contingency plans, such as Operation Cinder, which eliminated all but the most deadly and ruthless Imperials and planted the seeds for their return as The First Order. His machinations also resulted in the eventual corruption of Ben Solo, who would go on to lead both the marauding Knights of Ren (whose origins are unrelated to the Palpatine and the Sith) and the First Order itself.
In Legends, Darth Sidious often bent the late Darth Bane’s Rule of Two once he’d established the Galactic Empire and drove the Jedi to near-extinction. His Emperor’s Hands, the Imperial Inquisitors, and the Prophets of the Dark Side (originally a splinter religion from the Sith Order) were Sith in all but name. These powerful dark side users helped enforce his will during his reign as Emperor and ensured his legacy after his death. The Empire itself was fractured into various sub-factions led by Imperial Warlords after the Battle of Endor, eventually unifying into the Imperial Remnant in 12 ABY and formally surrendering to the New Republic in 19 ABY.
Kylo Ren
Originally the Jedi Ben Solo, the son of Han Solo and Leia Organa, Kylo Ren was gradually seduced by the allure of the dark side by the mysterious Snoke, leading him to nearly wipe out Luke Skywalker’s new generation of Jedi and join the Knights of Ren. Kylo killed and usurped the Knights’ leader and eventually did the same to Snoke, replacing him as Supreme Leader of The First Order.
Kylo Ren’s intrinsic strength in the Force astounded Luke, Snoke, and Palpatine alike, making his potential skill as a Jedi or dark side user highly sought after. Having been trained by Luke Skywalker himself in lightsaber combat, Kylo was extremely deadly against blaster-wielding opponents and other lightsaber wielders, as seen in Star Wars: The Rise of Skywalker where he fought against Rey and Alazmec cultists.
Snoke
The mysterious being known as Snoke unexpectedly took command of the Galactic Empire’s surviving forces and united them into The First Order, a military junta seeking to restore the Empire’s autocracy. What few in the galaxy knew is that Snoke is a strand cast, an artificially created humanoid, commissioned by Palpatine to take control of his Empire’s successor state. It’s not clear how much Snoke knew of his own origins, but he did possess free will, and he was instrumental in turning Ben Solo into Kylo Ren.
Though he isn’t a Sith or a Knight of Ren, Snoke was created by the Sith Eternal cult on Palpatine’s orders, and thus became an incredibly powerful unaffiliated dark side user. Snoke demonstrated terrifying strength in telekinesis, tossing around First Order General Hux and aspiring Jedi Rey with ease. Snoke was also adept at reading minds and ripping information from them, a skill he clearly passed down to Kylo Ren.
Ren
The first known Master of the Knights of Ren, the human known as Ren leads a small gang of dark side-using marauders through the treacherous charted but largely unexplored part of the galaxy known as the Unknown Regions. Ren’s philosophies, which were shared by his Knights and eventually Kylo Ren, differed from the Sith, as did their use of the dark side. Ren believed in listening to what he believed was the will of the dark side, going where it directed him, taking what it gave him, and destroying without remorse.
Ren and his Knights were undoubtedly powerful in the dark side, so much so that they were the subject of legends and horror stories about the dangers of the Unknown Regions. Their strength, however, was unrefined. Ren and followers were all easily dispatched by Luke Skywalker on Elphrona.
Lumiya
The Dark Lady of Sith Lumiya is, along with Palpatine himself, the closest person Luke Skywalker has to an arch-nemesis in the Legends timeline. Born as Shira Brie, the eventual Sith was originally an elite Imperial spy and was superlatively skilled as a soldier and pilot as a result. Under deep cover within the Rebel Alliance, Brie was able to join Rogue Squadron, consisting of the Rebellion’s best starfighter pilots. When her cover was eventually blown and her body ravaged when her ship was destroyed, Brie was rebuilt into a cyborg and trained as a Sith by Darth Vader himself, mirroring his own transformation in Star Wars: Episode III - Revenge of the Sith.
Unlike most Imperial dark side practitioners, Lumiya was a true Sith. As Palpatine and Vader both died during the Battle of Endor, she was on the Sith world of Ziost, completing her training and crafting her signature lightwhip (a whip-like lightsaber used by ancient Sith). After Endor, she established the next generation of Sith, reviving Darth Bane’s Rule of Two and orchestrating catastrophes from the shadows like Vader and Sidious. Lumiya’s strength as a Sith was surpassed only by Palpatine and Vader, with illusions and telekinesis being her preferred applications of the dark side. Lumiya was also an astoundingly skilled duelist, defeating Luke Skywalker less than a year after he bested Darth Vader himself, and being able to fight him on even terms decades later.
Cronal
Known by a variety of aliases, Cronal was the leader of the Prophets of the Dark Side, the Sorcerers of Rhand, and Imperial Intelligence. Cronal was a nihilist who was constantly awed by Palpatine’s talent for destruction. He was also the father of Sariss, another Prophet of the Dark side and one of Jerec’s followers. Though not a fighter, Cronal specialized in using the dark side to manipulate minds, inflict terror, and predict the future (which Palpatine found particularly useful). Like Palpatine, Cronal also mastered the rare ability to transfer his consciousness into another body, allowing him to cheat death.
Jerec
Originally a Jedi of the prequel trilogy era, Jerec did not fight in the Clone Wars, traveling to the Unknown Regions seeking ancient artifacts instead. Jerec returned to Coruscant shortly after the Empire rose and enacted the Jedi Purge. Jerec voluntarily joined the Empire, renouncing his ties to the Jedi and becoming both an Inquisitor and a member of the Prophets of the Dark Side. After the Battle of Endor, Jerec took command of a portion of the Pentastar Alignment (one of the Imperial warlord factions) and invaded the Valley of the Jedi on Ruusan, enhancing his power with the spirits of over a hundred Jedi and Sith.
Even without the Valley’s power, Jerec was a lethal warrior. A master of Makashi (the same lightsaber form that Dooku used), Jerec specialized in dueling other lightsaber-wielders. Though not as strong in the dark side as Vader or Lumiya (a fact that left Jerec with a bitter hatred of Vader in particular), Jerec was talented in a variety of dark side powers. Jerec paralyzed opponents with the dark side, mastered Force lightning, and often used Force destruction (a powerful blast of dark side energy).
Joruus C'baoth
An insane clone of a Clone Wars-era Jedi Master, Joruus C’baoth retained the arrogance of his clone template and then some, falling to the dark side and taking over the planet Wayland, subjugating its populace in the name of his twisted sense of justice. In the Thrawn Trilogy of novels, C’baoth established a (shaky at best) alliance with Grand Admiral Thrawn and extremely brief mentorship of Luke Skywalker (who believed him to be his clone template at first). C’baoth was a skilled practitioner of Force lightning and personal barriers, but his greatest strength was controlling the minds of others, which he often did to Thrawn’s subordinates.
Desann
Once an early member of Luke Skywalker’s New Jedi Order, Desann, who was ostracized for his powers in his youth, often bullied his fellow aspiring Jedi. When one student finally stood up to him, Desann murdered him and fled the Jedi Praxeum. Desann soon joined the Imperial Remnant and became a Sith in Lord Hethrir’s Empire Reborn sub-faction (it’s unknown if Hethrir was connected to Lumiya’s Sith Order). Desann was a formidable lightsaber wielder, using his natural Chistori strength to augment his melee skills. As a Sith, Desann was extremely skilled in telekinesis, Force lightning, casting illusions, and using the Force to strangle his enemies. At the peak of his strength, Desann was able to hold his own against Luke Skywalker for a few moments before retreating, a feat that few others could accomplish.
Darth Caedus
The oldest of Han Solo and Leia Organa’s three children, Jacen Solo was one of Luke Skywalker’s first Jedi students. As a young adult, he endured an entire year of constant torture as a prisoner of the Yuuzhan Vong during the Yuuzhan Vong War. Jacen turned to the dark side as a survival tactic, and he eventually joined Lumiya’s Sith after the war ended. Becoming Darth Caedus, Jacen’s remarkable natural strength in the Force was put to use as a Sith Lord.
Caedus was by far one of the deadliest dark siders in the galaxy after the original trilogy, almost rivaling his masters, Luke Skywalker and Lumiya. Caedus was not only more adept at controlling minds than even Joruus C’baoth, but he was equally proficient in blocking mental attacks from other Force users. Caedus was also a master of the iconic dark side powers of Force lightning and choking others. Most astoundingly, Caedus could use the Force to teleport objects and even move his consciousness into the past or future (flow-walking). As a duelist, Caedus was able to defeat the legendary Kyle Katarn, but could not overpower Mara Jade without gaining an advantage through casting illusions.
Abeloth
Far more powerful than any Jedi or Sith, the dark side entity known as Abeloth was a horrific creature who was held prisoner in the heart of The Maw, a cluster of black holes in the Outer Rim. An almost god-like entity, Abeloth had an almost omnipotent command of the dark side in all applications. As shown in the Fate of the Jedi novels, it took the combined efforts of the Jedi and Sith (including Luke Skywalker at the peak of his strength) to defeat Abeloth, but even so, they weren’t able to kill her.
Darth Sidious
Though he died during the Battle of Endor, Palpatine was able to come back from the dead in canon and Legends. Thanks to his apprenticeship under Darth Plagueis, Palpatine cheated death by transferring his consciousness into clone bodies.
Palpatine, a.k.a. Darth Sidious, was the galaxy’s deadliest Sith Lord who commanded the dark side with legendary strength. As a lightsaber duelist, Darth Sidious surpassed Yoda, (as seen in Star Wars: Episode III - Revenge of the Sith) and equaled Luke Skywalker (shown in Dark Empire). In addition to nightmarish Sith sorcery, Palpatine’s favorite use of the dark side was conjuring Force lighting to torture and kill his enemies. As shown in Star Wars: The Rise of Skywalker, he could create massive bursts of lightning that affected an entire fleet of ships. Even after he died in Return of the Jedi, Palpatine was the Star Wars franchise’s ultimate villain.