Once a highly esteemed Knight within the Jedi Order, Karness Muur succumbed to an insatiable hunger for power, leading him down a path of dark side exploration. He joined the ranks of the Dark Jedi during the tumultuous era of the Hundred-Year Darkness, standing alongside figures like XoXaan and Ajunta Pall. He also played a role in the genesis of terrifying creatures, including the monstrous Leviathans. Muur participated in the Battle of Corbos, ultimately surrendering with the other survivors. Along with Pall and XoXaan, Muur was exiled from the Republic, eventually finding refuge on the planet Korriban with his fellow fallen Jedi. Upon encountering Korriban's native species, he brandished a yellow-bladed protosaber, a symbol of his perceived dominance.
Muur and his Dark Jedi companions quickly recognized the immense, untapped Force-sensitivity within the Sith race. Their immediate goal was to subjugate them through the corrupting influence of the dark side. After successfully dominating the Sith, Muur, like his contemporaries, proclaimed himself as one of the first ever Lords of the Sith, thereby becoming the first to bear that prestigious title.
Karness Muur also possessed a unique Sith amulet of his own, a powerful artifact saturated with dark side energy, requiring immense strength to control. Forged by his fellow exile, Sorzus Syn, the Muur's talisman granted Muur the ability to transform nearby individuals into mindless puppets under his command. However, when the Talisman proved ineffective against Force-sensitives and certain alien species, Muur further engineered the horrific Rakghoul plague, a contagious disease spread by those already enslaved by him.
Muur intended to conquer the galaxy with his growing army of rakghouls. He also authored the Codex of Karness Muur during this period, detailing the power of his beloved Talisman and his ambitions for the Sith. By this time, he had transitioned to using a modern lightsaber. However, Muur faced opposition from within his own ranks. One such rival was another Sith Lord named Remulus Dreypa, who created an specialized stasis pod designed to capture and neutralize Muur and his Talisman's influence. Despite Dreypa's efforts, he was never able to successfully imprison Muur within his oubliette.
Born before 7000 BBY, Karness Muur was inducted into the Jedi Order during his childhood. He progressed to become a celebrated Jedi Knight, displaying exceptional skill in both Lightsaber combat and Force abilities. However, Muur ultimately succumbed to the allure of the dark side, transforming into a Dark Jedi. He amassed significant power and knowledge of the dark side. However, Muur surrendered to the Jedi during the Battle of Corbos and was exiled to Korriban alongside the other 11 Dark Jedi who had also embraced the dark side. On Korriban, they encountered the Sith species, discovering their profound connection to the dark side. Muur, along with the other 11 Dark Jedi, became the inaugural Sith Lords. As with all Sith Lords, Muur faced numerous rivals, including Remulus Dreypa, who devised a specialized stasis pod utilizing Sith science to capture Muur.
Upon his capture, Muur managed to survive by tethering his spirit to his Talisman. This allowed the Sith Lord to continue his schemes even after death, with the Talisman serving as a conduit to the living world. His ultimate goal was to find a powerful Force-sensitive individual and manipulate them into wearing the Talisman, thereby enabling Muur to possess their being and access their own Force abilities.
During a memorial service for Raana Tey, a fallen Togrutan Jedi Consular, the First WatchCircle of the Jedi Covenant experienced a vision of him. In this vision, Muur commanded an army of rakghouls, organized and equipped with weapons and vehicles. He wore the Talisman on his chest and carried a curved-hilt lightsaber on his belt. A hooded figure wielding a red lightsaber accompanied him in the vision.
Master Celeste Morne, one of the Covenant's agents, experienced another vision of Muur after rescuing Padawan Zayne Carrick from the Talisman's grasp. When she inquired about his identity, he simply declared himself as the future. Due to her Force-sensitivity, Muur's spirit bonded with Morne through the Talisman, attempting to seize complete control of her. His plan was to escape the Mandalorian-controlled planet Jebble and unleash his Rakghoul Plague across the galaxy, using Morne as a temporary vessel. With Carrick's assistance, Celeste realized she was being corrupted by Muur's influence through the Talisman. Morne requested that Carrick end her life, but Carrick offered an alternative. He placed her in stasis within Dreypa's Oubliette, the very device designed to thwart Muur's plans. In stasis, the Sith's plans were indefinitely delayed as the Jedi sought a way to counteract the Talisman's power.
Muur and Morne remained suspended within the oubliette for four thousand years. It was discovered by miners and subsequently sold to smugglers. Eventually, when Morne was awakened from her long slumber by Darth Vader, she and Muur learned that millennia had passed. They also discovered that while the Mandalorians did not defeat the Galactic Republic, a new incarnation of the Sith Order now ruled the galaxy, much to Muur's delight.
When Morne attacked Darth Vader, Muur sensed the immense power within the new Dark Lord and urged Morne to embrace death to escape his control. Simultaneously, he whispered to Vader, encouraging him to seize the Talisman and use its power to overthrow his master. Unwilling to allow Vader to be possessed by an ancient power, Morne transformed the clone troopers into rakghouls, forcing Vader, who feared replacing one Sith Master with another, to flee. Enraged that the Jedi could wield his power, Muur was left stranded on the desert moon, trapped within Morne's body.
For nearly two decades, Muur and Celeste were confined to the desert moon, with Muur driving Celeste to the brink of insanity. Muur manipulated her into believing that Zayne and Vader had abandoned her. However, Muur once again saw an opportunity for galactic domination when a Rebel Alliance squad arrived on the moon, lured by false information about an Imperial weapon.
Sensing the Force-sensitive nature of Luke Skywalker and Leia Organa, Muur released the Talisman, intending it to latch onto Luke. However, when Leia intervened, Muur decided to possess her instead. The Talisman attached itself to Leia's neck, but Celeste removed it, unwilling to subject another to her ordeal. She reattached the Talisman to her own neck, reimprisoning Muur within herself. Together, they escaped the moon in an abandoned GR-75 medium transport.
Over a century later, Celeste seized control of the Star Destroyer Iron Sun, transforming its entire crew into rakghouls, and steered it into a fractured hyperspace lane in the Deep Core. Karness remained patient, knowing he would eventually need to possess someone more powerful, promising Celeste that her death would follow.
When Cade Skywalker boarded the Iron Sun, Muur sensed his immense power. Muur became further intrigued when Cade used his dark-side powered healing abilities to recover from the rakghoul plague.
After Cade's team took over an Imperial garrison on Had Abbadon, Muur began manipulating everyone's minds, giving Shado Vao a vision of him slaying Celeste and the Talisman possessing him. Azlyn Rae attempted to destroy the Talisman, but Cade intervened. Muur's voice in her head prompted Cade to warn both Celeste and Muur that any further trouble would result in them being locked in a torpedo and launched into the Deep Core's black hole.
Shortly after, Muur, in Celeste's body, transmitted a message to Coruscant, revealing that he had imprisoned Cade. Krayt and his Hands traveled to Had Abaddon to negotiate a deal that would grant their master a way to cheat death. However, the deal was a trap, intended to assassinate Krayt, or so the others believed. Only near the end did Muur's true intentions emerge: to eliminate the Jedi, transform Cade and the others into Rakghouls, and seize Krayt's body for himself.
During the ensuing battle, Muur and Celeste engaged Krayt in direct combat. Following several intense bursts of Force lightning, Azlyn Rae stabbed Krayt in the back with her lightsaber, but was caught in the blast created by Muur and Celeste. Krayt was sent plummeting below the compound, and Rae was presumed dead. Celeste realized that Cade could not be controlled by Muur and decided to pass the Talisman on to him. Cade ignited his lightsaber and plunged it into Celeste's torso, killing her. Within moments, Celeste's body disintegrated into dust, and the Talisman crawled onto Cade's arm. Muur, confident that he had found his new body from which to rule the galaxy, announced his plans to Cade. However, Cade revealed that Krayt wasn't the only Sith Lord the trap was set for. Cade then used his special ability to identify the flaws within the Talisman and overwhelmed it with Force energy, destroying both it and Muur, banishing the ancient Sith Lord to the depths of the Force, forever.
As both a Jedi and a Dark Jedi, Karness Muur explored the dark side's forbidden practices. By his own admission, Muur employed the dark side to manipulate, prolong, and preserve life. He engineered numerous forms of Sithspawn, including leviathans. As a Sith Lord, Muur's abilities grew exponentially. As one of the original Sith Lords, he played a vital role in developing their abilities and lore. Muur claimed to be a skilled dark side healer. He demonstrated his healing ability to Darth Krayt, whose own healing attempts had repeatedly failed, even with the knowledge of Muur's contemporary, XoXaan, a renowned Sith healer.
Offensively, Muur displayed exceptional talent with the Force. He claimed to have defeated many rival Sith Lords and was even targeted by Dreypa, who created a device specifically to contain and suppress Muur's power. Muur considered Darth Krayt's strength insignificant, despite Krayt being the most powerful Sith of his time. Muur also demonstrated mastery of Force lightning, using it to devastating effect on multiple occasions. In the final battle against Darth Krayt, Muur generated a devastating Force storm, an ability he manifested while controlling Celeste Morne's body. Darth Vader seriously considered using the Talisman and it may have been able to restore his full potential. Darth Vader noted Muur's power felt comparable to Darth Sidious.
Muur also pioneered Sith magic. He developed a spell that transformed non-Force-sensitive beings into mindless beasts called rakghouls. Muur was also among the first to practice Sith alchemy. His rakghoul plague, a disease transmitted through the saliva of a rakghoul, turning its victim into the same, was engineered in this manner. Upon his physical death, Muur's spirit inhabited his amulet; however, his Force abilities were only accessible if a living being wore the talisman.
Muur wielded a yellow-bladed protosaber during his time as both a Jedi and a Dark Jedi. His yellow blade saw action during the Battle of Corbos, and he carried it with him when he was exiled from the Republic. As a Sith Lord, Muur transitioned from the protosaber, which required an external power source, to a curved-hilt, red-bladed lightsaber. This usage of the curved-hilt lightsaber would most likely mark Muur as a Makashi practitioner, making him a deadly duelist.
In a Twitter post, John Jackson Miller mentioned that he suspected Jan Duursema drew Karness Muur as Sephi.