The Dread War was a significant armed conflict during the larger Galactic War. It involved the Galactic Republic and the Sith Empire battling against the rebellious Sith Lords known as the Dread Masters. The battles took place on Oricon, a volcanic moon.
The six Dread Masters were exceptionally powerful Sith Lords directly subordinate to the Sith Emperor. They gained their fearsome title by mastering the Phobis devices, artifacts known to drive even the most corrupt Sith mad with terror. During the Great Galactic War, the Dread Masters utilized their skills in battle meditation to obliterate entire Republic fleets. They operated from an Imperial dreadnought until their capture in 3668 BBY by a team led by Jedi Knight Jaric Kaedan. The Jedi Order publicly announced the Dread Masters' deaths, but they were secretly imprisoned on Belsavis, a secret prison world.
A strike team from the Empire managed to infiltrate "the Tomb," an ancient section of Belsavis's deep prisons dating back to the Rakata Infinite Empire. They freed the Dread Masters, allowing them to return to the Empire's service. However, after the defeat of the Emperor by the Hero of Tython on Dromund Kaas, the Dread Masters turned against the Empire, aiming to seize control of the galaxy for themselves. In Section X on Belsavis, the Dread Host attempted to control an ancient Rakata weapon, the Aurora Cannon, but a strike team destroyed it. On Denova, they recruited the Trandoshan warlord Kephess and his Warstalkers to spread fear across the galaxy. On Asation, they activated a Gree hypergate to summon the "Terror from Beyond." Republic and Imperial forces eventually thwarted both of these operations.
Following the events on Asation, the Republic and Empire prioritized their ongoing conflict, including the campaign against the Hutt Cartel on Makeb and the investigation of the Czerka research facility on CZ-198. During the Makeb campaign, the Dread Masters reappeared. Lord Tagriss led a raid on the Arcanum, the Emperor's secret repository of Sith artifacts, and stole the Darkstaff and the Seeds of Rage. Agents working for either Darth Acina of the Dark Council or the Jedi Master Cedral Gend recovered the Seeds, which had been planted on various worlds. Tagriss was hunted down and killed in a corrupted Jedi temple on Ilum.
After his comrades repeatedly failed to coordinate their plans successfully, the Dread Master Styrak went his own way and started corrupting Darvannis, a Hutt world. He was eventually hunted down and killed there, marking the first death among the Dread Masters.
Following Styrak's demise, the Republic discovered the Masters' new operational base on Oricon, a volcanic moon located at the edge of Imperial territory. Six hours later, they dispatched a task force, led by Jedi Master Ogan-Dei, to bombard the moon from orbit and eliminate the threat. However, the Dread Masters used their dark powers to project terrifying images into the minds of the Republic forces, leading to the task force's destruction. Upon learning of the loss of contact with the task force, Supreme Chancellor Leontyne Saresh called upon Republic heroes to travel to Oricon and assist the survivors.
Shortly after, the Empire also uncovered the Dread Masters' location and the fate of the Republic task force. They sent their own force under the command of Lord Hargrev. Similar to the Republic, the Empire lost contact with its task force, as the Dread Masters' powers destroyed their ships. Darth Marr summoned the Empire's elite, who had been involved in the original mission to free the Dread Masters on Belsavis, to find Hargrev and determine the status of his forces.
Recognizing a shared enemy that neither faction could defeat alone, Republic and Imperial forces agreed to a temporary truce to combat the Dread Masters. Both sides worked to weaken the Dread Host, which ultimately led to an assault on the Dread Fortress, the Masters' base of operations.
Inside the Fortress, the Republic/Imperial strike team confronted Dread Master Brontes and her creations. The strike team battled many of Brontes' creations and servants, including Nefra, Qor'thest, Draxus, Grob'thok, and Corruptor Zero. After the strike team successfully defeated all of these opponents, Brontes faced them alone. Like Styrak before her, she failed and was killed.
Following Brontes's death, the team discovered a portal to the Dread Palace, the true base of the Dread Masters, and the hiding place of the remaining four. Each Master attempted to kill the strike team individually, but they all failed. Eventually, the strike team reached the Dread Masters' throne room, where the Masters mocked the team and predicted their deaths. However, surprised by the team's strength, they chose to recover their power. They summoned the spirits of the deceased Dread Masters Styrak and Brontes to aid them in battle. The strike team defeated them easily. Realizing they might actually die, the living Masters sacrificed some of their life force in a desperate attempt to destroy the strike team. The strike team was taken aback, but proceeded to strike down each Dread Master one by one.
The Dread Masters' rogue actions and terrifying schemes were finally brought to an end. The greatest threat to galactic stability had been eliminated.
The Republic strike camp received an unexpected visitor: Dread Master Calphayus. Calphayus had survived his death for reasons unknown, even to himself. He explained that he remembered what it was like to no longer be afraid and that upon his near-death, saw light. He explained that he was no longer bound to the other Masters, as he had been previously. The Republic strike team showed mercy and spared his life, and Calphayus was taken away to be treated by the Jedi.
The Dread War is featured in the video game Star Wars: The Old Republic through daily single-player missions and an 8-16 player operation. It was introduced in "Game Update 2.4: The Dread War" released on October 1, 2013.