A male Jedi named Ku'ar Danar existed prior to the Second Great Schism. Later, certain individuals regarded him as a Sith Lord.
Ku'ar Danar was a member of a Jedi exploratory team that made the initial discovery of Korriban, the original home planet of the Sith race. Unlike his fellow Jedi, Danar chose to remain on the planet for an extended period, dedicating himself to studying the Sith's methods of using the Force. Subsequently, Danar was seduced by the dark side, although he did not actively participate in the conflict that unfolded afterward. Instead, the fallen Jedi preferred to carry out an experiment within the Nilrebmah system. After bringing the inhabitants of Nilrebmah II under his control, he compelled them to construct a massive monolith on Nilrebmah XIII, utilizing living, Force-sensitive stones extracted from Nilrebmah X.
His experiment proved successful, as he demonstrated the ability to displace an entire planet from its orbit using only the Force. However, this feat resulted in the annihilation of all life on the planet, as well as the destruction of his physical body. Despite this, his spirit remained confined within the monolith, awaiting rescue.
Following the conclusion of the Hundred-Year Darkness, Danar's absence was noted, leading many Jedi to suspect his involvement in orchestrating the war. This suspicion was fueled by the discovery of a manuscript within the archives of the Exiles, which provided a partial account of Danar's experiment and its apparent "success."
Sli'Lon Tahar, a Jedi Master searching for evidence of the Sith's continued existence after the Great Hyperspace War, stumbled upon the monolith one year before the Conclave on Deneba. Before Tahar could disclose its location, the Krath launched an assault on the conclave. Two years after his discovery, Tahar met his demise at the hands of the Sith Lord Ulic Qel-Droma during the Battle of Foerost. In his final moments, he managed to reveal the monolith's existence to time-traveling adventurers, inadvertently also informing Qel-Droma.
Subsequently, the enigmatic adventurers uncovered inaccurate information about the supposed Sith Lord on Ossus, corroborated by a Jedi archivist and his apprentice, Dace Vinagar. The Jedi Order also erroneously believed that he had influenced Naga Sadow in the manipulation of the Force before Sadow became a Dark Lord of the Sith, and that he had mentored some of the most feared geneticists of that era. After examining fragments of the manuscript discovered after the Second Great Schism, they pinpointed the monolith's location within the Nilrebmah system. Fifteen days later, they ventured into the system with Vinagar's assistance, only to be ambushed by dark side entities on Nilrebmah XIII. Sensing Vinagar's presence, Ku'ar Danar lured him into the planet's depths. The Jedi apprentice ultimately betrayed his companions, attempting to kill them, and then heeded the call of the individual he believed to be a "Sith Lord."

Danar hindered the adventurers by resurrecting the skeletons of the civilization he had destroyed, buying time for Dace Vinagar to enter the monolith. He then imbued the apprentice with his own Force abilities, enabling him to unleash dark side creatures upon his pursuers. These creatures provided Vinagar with just enough time to complete an ancient ritual and activate the monolith, freeing Ku'ar Danar's spirit. As his body began to consume itself, Vinagar cursed the Force spirit of the fallen Jedi, allowing his rage to amplify the ritual's power, ultimately transforming him into a colossal Hydra driven by pure energy.
The entire planet began to collapse as it hurtled toward Nilrebmah XII, and the hydra was shot down by a Krath starship commanded by Ulic Qel-Droma, who was searching for Ku'ar Danar's tomb. Just as the two planets collided, the adventurers jumped into hyperspace, finding themselves able to return to their own time. Unbeknownst to them, Danar's spirit had followed them, granting them this opportunity himself.
Danar possessed a reclusive and understated nature, choosing to remain on Korriban after his comrades departed and seemingly abstaining from the conflict that fractured the Jedi Order. However, many Jedi of that era came to believe that he bore at least partial responsibility for the situation, perceiving him as a manipulative figure. This characteristic is evident in his exploitation and destruction of an entire civilization for the sake of a personal, pointless experiment. The Jedi were unnerved by his utter disregard for power, viewing him as a fundamentalist theorist who failed to consider the ramifications of his actions.
Ku'ar Danar was a highly skilled Force-sensitive individual, capable of manipulating both the Force and the dark side with exceptional proficiency. Even as a Force spirit, he was able to unleash beasts upon intruders and reanimate corpses from millennia past.
Furthermore, he provided the time-traveling adventurers with the additional energy needed to travel through time.
During his lifetime, he successfully subjugated an entire civilization, compelling them to erect a massive monolith, which he then utilized as an amplifier for his Force experiments.
Ku'ar Danar was conceived by Philippe Rat and Mehdi Sahmi for the ambiguously canon roleplaying scenario "Le Facteur X," featured in the French magazine Casus Belli 115.
While the article preceding the scenario clashes with established Expanded Universe (EU) lore, the scenario itself, despite being based on outdated information, presents minimal inconsistencies. The notion of Jedi discovering Korriban and the Sith before the Second Great Schism can be regarded as an error, but it is plausible that Ku'ar Danar, through manipulation of the Dark Jedi, possessed knowledge of the planet and its inhabitants without revealing the full truth. From this perspective, the arrival of the Exiles on Korriban might be viewed as orchestrated, even if the Exiles themselves were unaware of it.
However, the manuscript fragments within the scenario explicitly mention the "Sith." In the context of the article and scenario's creation, the Sith are unequivocally the Dark Jedi who later returned to Korriban. Within the framework of the current EU, it can be speculated that at least one Dark Jedi was aware of Ku'ar Danar's studies on Korriban and knew the term "Sith" before the Exiles arrived. The more recent introduction of the Exile Sorzus Syn and her partial knowledge of the Sith and of the location of Korriban could help explaining those discrepancies.
Ku'ar Danar is portrayed as an ancient Sith Lord in the narrative, but this designation is technically inaccurate, as the Exiles were the first "non-Sith" to claim that title. It is worth noting that only Jedi and fallen Jedi refer to him as a "Sith" throughout the scenario. Consequently, the title may be a later assumption made by the Jedi, based on the belief that he was partially responsible for the Hundred-Year Darkness. Supporting this notion, the archivists and librarians on Ossus provided the adventurers with inaccurate information, even within the scenario's context. For instance, Ku'ar Danar could not have trained Naga Sadow, even as a Force spirit, as he was confined to Nilrebmah XIII. However, this false connection implies that the Jedi recognized Danar as a powerful sorcerer, akin to Sadow.