The Sith Brotherhood, also known as the Brotherhood of the Sith, was a faction of Jedi Knights who, under the leadership of Dark Lord of the Sith Exar Kun, seceded from the Jedi Order with the intention of delving into Sith techniques. During the period of the Great Sith War, they established a Sith Empire that garnered the support of both the Krath and the Mandalorian Crusaders commanded by Mandalore the Indomitable.
On Ossus, Exar Kun, the Dark Lord of the Sith, delivered a passionate address that initiated the first doubts among his fellow Jedi Knights. Following the demise of Arca Jeth on Deneba, numerous Knights experienced a disenchantment with the Order, abandoning their idealistic views regarding the Jedi's immortality. Driven by concerns for the future's security, a number of Jedi Knights found themselves persuaded by Exar Kun's assurances of accessing additional "lost" Jedi powers.
Regrettably for these young Knights, Exar Kun's focus was not on the Order's future; instead, he had journeyed to Ossus with the goal of assembling a formidable cadre of commanders to lead his forthcoming conflict against the Republic. Kun's expedition to Ossus was motivated by dual purposes. In addition to recruitment, Kun was determined to acquire the renowned Sith holocron held by Odan-Urr. Forcibly entering Odan-Urr's sanctuary, Kun murdered the elderly Jedi Master and seized the ancient holocron for his own use.
Upon being discovered in the act of taking the artifact, Kun deceived his newfound adherents by asserting that Odan-Urr had proclaimed him a Jedi Master and had bequeathed the artifact to him as a symbolic gesture of his induction, just before succumbing to old age. With the growing admiration of his fellow Knights, Kun boarded his vessel, the Starstorm One, accompanied by his twenty knights, and departed for Yavin 4, a location saturated with dark side energy.
Prior to his speech on Ossus, Exar had already been to Yavin 4, where he had subjugated the indigenous Massassi population. Through exploration of the planet's ruins and excavation efforts, he uncovered the final resting place of the Dark Lord of the Sith, Naga Sadow. Utilizing the Massassi's labor, Kun erected numerous temples across the planet to amplify his own Force abilities. It was into this setting that Kun and his followers arrived.
Upon their arrival on Yavin 4, the twenty knights dispersed, becoming increasingly uneasy due to the palpable dark presence pervading the planet. Leading the group to the main Sith Temple, Exar declared the dawn of a new era for the Jedi Knights, one characterized by the rediscovery of forgotten techniques.
One Jedi Knight, Oss Wilum, felt profound revulsion at Kun's apparent obliviousness to the dark aura emanating from the planet's surface. He distanced himself from the other admiring followers and attempted to leave the planet, only to be abruptly intercepted by Massassi warriors. The other Knights rushed to his defense, and it appeared as though the Brotherhood would dissolve before it could even materialize. However, through quick thinking, Kun salvaged the situation. Deceiving his followers once more, Kun halted the attack by claiming that he was aware of the dark power originating from the planet and required the assistance of the other Knights to cleanse the world of the dark side.
Recognizing that Oss Wilum's outburst was unlikely to be an isolated incident, Exar expedited the indoctrination process. Employing the Sith holocron he had pilfered from Odan-Urr, Exar Kun shattered the artifact, asserting that he was doing so to eliminate its dark influence. In actuality, this action unleashed the dormant teachings of the Sith Lords contained within. The shards from the shattered device became embedded in Kun's followers. Functioning as a form of Sith poison, the Knights' emotions were completely distorted, and their reservations about Kun and the dark planet dissipated. Thus, the Brotherhood was truly established.
Following extensive training on Yavin IV, Exar's Sith Order had fully embraced their newfound path. Confident in their capabilities, Exar was prepared to initiate his plan. With the approval of his Sith brethren, Exar denounced the Jedi Masters as heretics who refused to acknowledge the truth of the new way. He claimed that the old ways must be eliminated before the Sith Golden Age could commence. Exar dispatched his Sith disciples on their inaugural mission: to exterminate their own Jedi Masters.
The insurrection proved to be a resounding triumph for the Brotherhood and their burgeoning Sith Empire. Nearly all of Kun's disciples succeeded in their missions, catching their masters off guard with the novel Sith techniques imparted to them by Exar. However, some masters possessed sufficient skill to recognize the corruption within their students and were prepared. Master Thon successfully repelled both Oss Wilum and Crado when they employed the Force to summon vicious Hssiss dragons against the Tchuukthai Master. Crado managed to escape, but Oss was captured. Zona Luka succeeded in killing Master Dominus but was also killed in the process. Nayama was unable to kill her master Jolee Bindo during their confrontation and fled in disgrace.
With the Jedi leadership in disarray, Exar launched his next offensive against the Republic. Resolved to completely dismantle the Jedi Order, Exar plotted to destroy the Jedi Library on Ossus. After uniting with his apprentice Ulic Qel-Droma, Exar discovered the treachery of Ulic's illicit lover, Aleema Keto. Exar devised a scheme to eliminate this nuisance and ensure the Jedi's demise. By manipulating the treacherous Aleema and the cowardly Crado to trigger a supernova in the Cron Drift, Exar orchestrated the destruction of Ossus. Both Aleema and Crado perished in the supernova as a consequence of their failures.
As the Jedi attempted to evacuate Ossus, Exar, Ulic, and the remaining members of the Brotherhood landed on Ossus with the intention of seizing as many Jedi artifacts as possible. The raid proved highly successful but suffered a significant setback when Ulic was shot down by his brother Cay and taken prisoner. Following Ulic's capture, Exar retreated to Yavin IV, pursued closely by the Jedi. With a wall of light directed at the planet, the entire world was engulfed in flames. Exar was presumed dead as a result of the fires, and the war was declared over.
The Sith Academy established by the Brotherhood of the Sith remained operational following the Great Sith War. This academy would play a vital role in the Jedi Civil War when the new Dark Lords of the Sith, Darths Revan and Malak, required a readily available source of Sith disciples for their own Sith Empire.
Several other Jedi are depicted undergoing training on Yavin IV, but their identities remain unknown at this time. The video game Knights of the Old Republic introduced the Rodian character Suvam Tan, who claimed to have been a Sith slave on Yavin IV. However, the comic depicts no slaves on the planet other than Massassi. It is also established that Suvam constructed a lightsaber and possessed a Sith holocron and Exar Kun's armor at the time of his death. Based on these possessions, it can be inferred that Suvam was likely affiliated with the Brotherhood. Nevertheless, concrete evidence remains lacking.