Dromund Kaas operation

In 4999 BBY, the Sith Lord Vitiate used a ritual of Sith magic to consume the life of all beings on his homeworld of Nathema. The casting of the ritual stripped the Force itself from the entire planet, killing every living being on Nathema and allowing Vitiate to consume their combined life force, granting him immense strength in the Force and rendering him immortal. Now known as the Sith Emperor, he went on to reconstitute the Sith Empire, over which he ruled for well over a thousand years. Throughout that time, the Emperor delved further into the study of Sith magic, seeking a way to gain even more power.

In 3950 BBY, the Emperor was attacked by three powerful Force users—the Jedi Revan and Meetra Surik and the Sith Lord Scourge—and was almost defeated by them. However, during the fight, Scourge had a vision of the future, where he saw another Jedi standing victorious over the Emperor. He chose to betray Revan and Surik in order to ensure that future came to pass, as he understood the threat that the Emperor posed to the galaxy.

As a result, Scourge was appointed as the Emperor's Wrath, the Emperor's personal enforcer, and served the Emperor for the next few centuries, while Surik was killed and Revan was captured and tortured during the same period. Due to the Emperor's brush with death, he sought out a way to transfer his consciousness and powers between host bodies, and the Emperor thereafter used them in order to safeguard his true body from harm. Among Imperials, the host body was known as the Emperor's Voice.

In 3641 BBY, the Galactic War broke out between the Empire and the Republic, largely thanks to the Republic's freeing of Revan—in his captivity, Revan had used the mental link between him and his captor to temper the Emperor's desire to destroy the galaxy. As war broke out, the Emperor began preparations to repeat his ritual on a galactic scale, intending to consume the entire galaxy as he had Nathema. Around a year later, he dispatched a number of Sith and Dark Jedi agents to various worlds in order to perpetrate a mass death of thousands of beings, as his ritual would require a sacrifice to begin. However, Scourge betrayed the Emperor and sought out the Jedi from his vision, a Jedi Knight known as the Hero of Tython.

Scourge informed the Jedi Council of the Emperor's plans and allied with the Hero in an effort to prevent the ritual. With Scourge's aid, the Hero foiled the Emperor's efforts on the planets Belsavis, Voss, and Corellia, and the Emperor's agent on Corellia, the Dark Jedi Tol Braga, gave the Hero the Emperor's coordinates on the Imperial capital world of Dromund Kaas. With the Emperor's location in hand, Grand Master Satele Shan of the Jedi Order decided that the time was right to strike against the Emperor before he could achieve the sacrifice necessary for his ritual. Therefore, she assembled a combined task force of Republic Navy and Jedi warships for an assault on Dromund Kaas and tasked the Hero and their crew of allies with infiltrating the capital and eliminating the Emperor.

Upon arriving in the Dromund system, the Republic task force immediately engaged the Imperial First Defense Fleet, drawing the majority of the Imperial forces in the system to them. Under cover of the fighting, the Hero's crew entered Imperial airspace and landed their Defender-class light corvette on the outskirts of Kaas City. The Hero's crew consisted of six individuals—the Hero, Lord Scourge, Jedi Knight Kira Carsen, the combat medic Archiban Kimble, the Republic trooper Fideltin Rusk, and the astromech droid T7-O1. Acting on Scourge's knowledge of the city, the group determined that the easiest way to the Emperor, who was located in the edifice known as the Dark Temple in the nearby jungle, would be to steal one of the Emperor's private shuttles that were docked in the city.

The group broke up into three pairs of two and fought its way through Kaas City, which at the time was lightly guarded by Imperial soldiers, Imperial commandos, Mandalorian mercenaries, and war droids, including a massive Imperial Ravager Droid. All three pairs made it safely to the shuttle, where they discussed their plan of attack before departing. Because of the Emperor's power, none of the others could safely accompany the Hero into battle with the Emperor for fear of being controlled; however, because T7-O1 was a droid, he could face the Emperor without being in danger of manipulation. The other four would engage the temple's defenders in order to draw opposition away from the Hero and T7-O1 and clear their path to the Emperor. Scourge flew the shuttle to the Dark Temple, which the six stormed to battle the dozens of Imperial Guardsmen and Sith assassins who guarded the edifice and their Emperor.

Despite the enemy's numbers, the Hero and T7-O1 soon reached the stairs to the upper levels, where the Emperor waited; however, as T7-O1 interfaced with the temple security system and deactivated the force field that blocked the stairwell, he detected that one of the Hero's companions was about to be overwhelmed by Imperial Guard reinforcements nearby. Unwilling to let one of the others be killed for the sake of the mission, the pair rushed to their ally's aid, eliminating the numerous Imperial Guards and rescuing their companion before returning to the stairwell and continuing toward the Emperor. Confident in his power, the Emperor awaited the Hero's arrival in one of the temple's upper chambers and was unconcerned when the Jedi and T7-O1 succeeded in breaching his sanctum.

The Sith greeted his enemy with a bolt of violet Force lightning, mocking the Hero for sacrificing strength to rescue an ally. The Hero intercepted the lightning with their lightsaber blade, and the Emperor then summoned three phantom duplicates of himself that attacked the Knight and droid as the Emperor descended from his throne to confront his enemy. The pair made quick work of their phantom opponents, and when the Hero then questioned the Emperor's desire to consume the galaxy, the Emperor scoffed at what he saw as the Jedi's limited grasp of reality—he intended to outlast everything, and there were more galaxies and universes for him to conquer beyond their own.

The Sith then summoned several more duplicates of himself and drew his own lightsaber, and the numerous Emperors attacked their opponents. The Emperor and his copies utilized Force lightning and Sith magic as well as their lightsabers in battle, disappearing and reappearing throughout the chamber to toy with the Jedi's senses. However, the Hero and T7-O1 stood strong against their opponents, and one by one the Emperor's duplicates fell until the remaining duplicates vanished in swirls of dark side energy as the true Emperor fell to his knees. The Hero charged the Emperor, intending to end their battle, but the Sith ruler unleashed an explosive blast of Force lightning that threw his enemy across the room. Acknowledging the Hero's strength in the Force, the Emperor cast another burst of Force lightning directly at the Jedi, only for them to catch the attack on the blade of their lightsaber.

As the Emperor continued to generate lightning, the two enemies advanced on each other from across the room, but when they reached each other, the Hero spun out of the way of the lightning and dealt the Emperor a devastating blow to his waist. The Sith ruler collapsed to the floor. However, as he tried—and failed—to rise, he declared that he would never be contained or redeemed and scoffed at the Hero's claims that he would be taken to Tython and turned from the dark side. The Hero then contacted Scourge and reported success, but Scourge warned his ally that the Emperor was not yet dead.

Scourge was correct—the Emperor's essence left his fallen Voice and, warning the Hero that he would take his enemy with him if he was going to die, released a massive amount of dark side energy from the Voice as a final act of defiance. The released energy severely damaged the Dark Temple, causing the upper levels to begin collapsing, and the Hero and T7-O1 rushed out of the temple to safety. The pair met up with the other members of their group, who had all survived their battle with the temple's defenders, and flew the Emperor's shuttle back to Kaas City and boarded their own waiting ship outside of the capital. Upon lifting off, the Hero immediately contacted the Grand Master and reported the mission's success, leading Shan to order a general retreat from the Dromund system.

The remaining ships of the task force rendezvoused at the Republic cruiser Valiant near the Core Worlds, where Admiral Dabrin of the Republic Navy and the Grand Master arranged an award ceremony for the Hero and crew. All of the group received the Cross of Glory, the Republic's highest honor, and Shan elevated the Hero to the rank of Jedi Master.

With the loss of his Voice, the Emperor's essence retreated to his true body, where he entered restorative hibernation to recover from his battle with the Hero. Rumors of the Emperor's death spread among the upper levels of the Sith Empire, leading the maverick Sith Lord Darth Malgus—already disgusted with the Empire's anti-alien policies and the infighting exemplified by the Empire's ruling Dark Council—to rebel at the Battle of Ilum not long afterward. Seizing the Emperor's abandoned space fortress, Malgus declared a New Empire, splitting the forces of the Empire as many defected to his cause.

The New Empire was crushed at the Battle of Ilum by both the Republic and the Empire, but the damage was done—combined with the recent loss at the Battle of Corellia, the Empire, which had previously held the upper hand in the Galactic War, was gradually forced on the defensive. The veteran Dark Councilor Darth Marr eventually assumed a leadership role in the Empire and made efforts to restore Imperial supremacy, but it was not until around 3638 BBY, after the Hutt Cartel's failed invasion of the planet Makeb, that Marr halted the Empire's losses when he acquired the powerful mineral known as isotope-5.

The details of the Dromund Kaas operation, as the event came to be known, were highly classified by the Republic. The newly elected Supreme Chancellor of the Republic, Leontyne Saresh, refrained from announcing the operation to the public initially, but she immediately adopted an aggressive stance against the Empire, appointing the veteran soldier Jace Malcom as Supreme Commander of the Republic Military as part of an effort to take the fight to the Empire. A joint committee of Jedi and agents of the Republic Strategic Information Service, the Republic's intelligence agency, was tasked with confirming the Emperor's death.

As the Emperor's Hand, his most trusted servants, were tasked with guarding the Emperor's body, only they and the new Emperor's Wrath were aware of the Emperor's survival; thus, the committee's conclusion was that the Emperor was indeed dead. In the aftermath of the Republic's victory over the Hutt Cartel at Makeb, the Chancellor, Shan, and Malcom held an official announcement of the Emperor's death on the HoloNet.

The Emperor's essence was severely injured by the battle with the Hero and thus was forced into hibernation in his original body. While he slumbered, his consciousness reached out to his Children—agents of the Emperor's will who were mentally linked with their "father." The Emperor's pain and anger led him to issue crazed and conflicting commands to his children, such as "freeze the oceans of Manaan" and "set fire to Ord Mantell," calling for the destruction of entire worlds. Unable to handle the influence of their injured Emperor, a number of Children were driven near insane; others managed to shut out their master's commands, shielding themselves from his damaging influence until he healed.

The Emperor's apparent death and resultant hibernation had another major effect on the galaxy: the six Sith Lords known as the Dread Masters, who had served the Emperor for centuries, were left without the Emperor's guidance and commands. Incredibly powerful in the Force, the Dread Masters found that none in the Empire were powerful enough to command their loyalty and thus decided to make the galaxy their own. Wielding their power over fear and the minds of others, the Dread Masters gathered an army of their own and set about acquiring exotic technology from species such as the Rakata and the Gree, becoming a third power in the Galactic War. Their attacks on Hutt Space led the Hutt Cartel to try and expand their borders in order to make up for lost territory, and the Hutt Cartel's expansions led to the death of the Cartel's Supreme Mogul, Karagga.

Karagga was succeeded as Supreme Mogul by Toborro the Hutt, who instigated the Hutt invasion of Makeb in 3638 BBY. Shortly afterwards, the remaining Dread Masters sank into insanity and decided to destroy the galaxy, though they were ultimately defeated at the moon of Oricon. In the depths of Wild Space, the Sith Emperor's biological daughter, Vaylin, discovered that the mental barriers her father had installed in her mind to prevent her from utilizing her full power were gone. With that discovery, Vaylin began plotting her revenge against her father. The Emperor's spirit went on to serve as a major player in the galactic conflicts that followed, although it was not until 3626 BBY that his spirit was finally vanquished for good.

The Dromund Kaas operation served as the focus of the Jedi Knight class's finale mission, "Doomsday," in Star Wars: The Old Republic, a massively multiplayer online role-playing game released by BioWare in December 2011, although it first appeared as a vision to Lord Scourge in the prequel novel The Old Republic: Revan, written by Drew Karpyshyn and published on November 15, 2011. The mission is identified as the "Dromund Kaas operation" by the droid RL-4, who introduces the Karagga's Palace Operation for Republic players, and The Old Republics Digital Expansion Rise of the Hutt Cartel features Chancellor Saresh's official announcement of the Emperor's death.

In "Doomsday," the player is presented with the choice of saving an imperiled companion, gaining light side alignment points, or continuing on to fight the Emperor, thus depriving the Emperor the chance to gather more strength and gaining dark side alignment points. The companion in question will be the companion with which the player has the highest Affection points, excluding Lord Scourge and T7-O1, and there is no difference in difficulty in the fight with the Emperor between the two choices. If the player does not rescue the companion, then the character is rescued by one of the player's other companions. At the award ceremony, the player will either be awarded the rank of Jedi Master or general depending on whether the player has a light or dark side alignment score, respectively. As the Jedi Knight is a Republic-class character, this article assumes that the player chooses the option that results in the most light side points; thus, the Hero of Tython is assumed to have rescued the companion and became a Jedi Master.

• Star Wars: The Old Republic Encyclopedia