Kopecz was a male Twi'lek, born on the planet Ryloth during the New Sith Wars. In his native language, Kopecz's name translated to "philosopher," and was popularly given to males of hisspecies. A force-sensitive, Kopecz became a member of the Jedi Order, and trained for a number of years. Over time, Kopecz became increasingly disillusioned with the Order, and eventually rejected their philosophies for the ways of the of the dark side. With the Sith ascendant across the galaxy, Kopecz defected, believing that they seemed to offer the best chance to build a stable galaxy. During his time as a Sith, he struck up a fierce rivalry with Qordis, a human dark lord.
Fights between Lords in the same vein as that between Kopecz and Qordis were common among the Sith, as each individual Lord sought sovereignty over all others. It was during this time that a charismatic Dark Lord named Kaan formed the Brotherhood of Darkness, where each minor Lord would be elevated to the title of Dark Lord of the Sith, and all would pool their resources into one united front. With the Sith at war with both the Galactic Republic and the Jedi, Kaan realized that infighting between fellow Sith Lords would only result in defeat from within their ranks. Recognizing both men as assets to the Sith war effort, Kaan appealed to Kopecz, as well as Qordis, to join his new Brotherhood. Both accepted Kaan's offer, and the newfound equality that the Brotherhood professed was enough to maintain an uneasy truce between the two. In 1,006 BBY, the three Dark Lords planned to retake Korriban, the ancient homeworld of the Sith, to reestablish the ancient Sith Academy there where future Dark Lords for the Brotherhood could be trained. In a fierce ground battle led by Kaan, Qordis, and Kopecz, the Sith were victorious against the Jedi and Republic; the aftermath saw Qordis remain on Korriban to oversee the Academy's reopening, where he would also serve as headmaster. Kopecz, however, remained with Kaan to continue the war against the Republic.
Kopecz was one of the Sith Masters present at several battles during the New Sith Wars—though the Brotherhood promised equality as Dark Lords, in practice there were always Masters who took up the roles of leadership, conveying orders between Kaan and the other Dark Lords. Kopecz was one such leader, serving as commander during the Battle of Phaseera. There, he had control of all military units on the world, including the Brotherhood's specialized unit of Gloom Walkers. An incident broke out in that unit, when Gloom Walker sergeant Dessel knocked his commanding officer, Ulabore, unconscious and assumed command of the squad. Dessel had acted with the intention of saving his squad from a suicide mission that Ulabore had accepted; under Dessel's command, the Gloom Walkers disobeyed specific parameters set for their mission, but nonetheless successfully completed it with minimal casualties. Despite the success of the mission, Kopecz was charged with overseeing disciplinary action against Dessel for his actions. However, he sensed the power of the Force within Dessel and also reviewed his file, which had various accounts of the Human's seemingly amazing feats. Kopecz opted not to court martial him and instead took him to Korriban, where he told the Human soldier he was to be trained as an apprentice with the capability of becoming a Sith Lord. In response, Dessel assumed the name Bane—Bane of the Sith.
Kopecz was one of the Dark Lords present at the first battle of Ruusan, when the Brotherhood launched a surprise counter attack against the Republic forces that had been performing hit-and-run strikes on the Sith-occupied world of Kashyyyk. During the battle, he flew his Sith Buzzard starfighter and was aided by the battle meditation that Kaan provided from aboard the Sith Destroyer Nightfall. While egaging enemy fighters, Kopecz sensed the Republic pilots were being aided through the Force. Realizing that there must be a Jedi Master using battle meditation somewhere aboard one of the capital ships, the Twi'lek detected the source and flew into the hangar bay. Infiltrating the ship, the Sith Lord slew all in his path, reaching a chamber where he discovered a female Cerean Jedi Master deep in meditation, guarded by two Selkath Padawans. Killing the aspiring Jedi and the Master restored the Sith advantage and turned the tide of battle their way, resulting in the eradication of the Republic forces.
In the second of the battles for Ruusan, the Republic sought to reclaim the planet from the Sith. Unable to achieve victory in just one skirmish, their offensive was finally successful in the third battle; Kopecz was responsible for informing Kaan of the Sith defeat, when the Jedi Order's Amy of Light revealed itself for the first time. The battle also revealed the location of the elusive Lord Hoth, the leader of the Army of Light and the only commander that seemed capable of solidifying victories against the Sith forces. Kaan moved the majority of the Brotherhood of Darkness to Ruusan, calling all the Force-sensitives under his command, save the strongest apprentices on Korriban who had not yet completed their training.
The Sith then engaged the Republic in two more offensives on Ruusan, but it soon became apparent to Kopecz that their forces were drastically outnumbered, thanks to the addition of Hoth's Jedi army. When planning the Sixth Battle of Ruusan, Kaan originally intended for Kopecz to lead a flanking maneuver to attack the Jedi. This was before the return of Darth Bane—the apprentice had left the Brotherhood of Darkness, assuming the abandoned "Darth" title, and survived two attempts on his life by Sith Lords Kas'im and Githany under Kaan's orders. Bane accused Kaan of being too merciful, proposing that the Sith forces, instead of circumventing the forest in which the Jedi were hiding, destroy it completely. Kopecz and the other Sith Lords agreed to the plan, and with Bane leading them, they unleashed a massive firestorm on the forest, inflicting heavy losses on the Jedi forces.
After the destruction of the forest, Kopecz commented on Bane's channeling technique, stating it felt as though Bane's teeth were in their throats. Kopecz and the other Dark Lords feared Bane's power; and the Twi'lek made the Human aware of it. Kopecz then mounted his flyer and took off for the battle, which he expected to result in a victory for the Sith. However, the intervention of gunships bearing the colors of Jedi Master Valenthyne Farfalla and the reinforcements he had brought from the Republic and the Jedi Order forced the Sith to retreat.
Following their defeat, Kopecz learned of Kaan's new plan: to create an ancient Sith weapon called the thought bomb that destroyed every Force-sensitive in the vicinity, and wipe out the Jedi once and for all with it. The Twi'lek questioned Kaan's sanity, for the latter believed that the combined power of the Dark Lords would be enough to survive the ancient Sith ritual. As he sat in the cave where Kaan had his minions gathered in preparation of the bomb, Kopecz encountered the newly-ordained Dark Lord Githany and her apprentice Darovt, who immediately turned around and fled with the boy after hearing from Kopecz of Kaan's purported madness. Kopecz also recognized Kaan's lunacy, but he was nevertheless coaxed into joining the other Dark Lords in creation of the thought bomb by Kaan, who was manipulating them all through the Force. However, when the congregation finally began to chant, Kopecz regained his senses. Fearful of the effects of the bomb, he realized that it would destroy the entire gathering of Sith as well as the Jedi. Kopecz knew that by this time the Jedi would have the caves surrounded, and that one way or another, he would not survive. He decided instead to join the Sith warriors who were ordered to defend the caves and fight with them.
Kopecz arrived above ground in time for the final battle, where he became critically wounded, though he continued to fight until the end. The Sith had lost to the combined forces of the Army of Light and the Republic, who were under the leadership of Valenthyne Farfalla, and most of the regular Sith troops surrendered instead of being killed. Kopecz refused to submit, despite the Jedi's apparent victory; the Twi'lek made this clear when he confronted Farfalla, and refused to be taken alive. Spurning all help, Kopecz offered to reveal Kaan's plans in exchange for the promise of death in combat. Upon Farfalla agreeing to those terms, Kopecz informed him of the thought bomb and the madness Kaan had descended into. Honoring his word, Farafalla then engaged Kopecz in lightsaber combat—the injured Dark Lord was no match for his freshly arrived opponent, and was slain.