Battle of Ossus ( Great Sith War ) The Battle of Ossus took place in the year 3996 BBY during the Great Sith War , and was one of the last major battles to be fought during that conflict . With Aleema Keto ' s destruction of the Cron Cluster through the use of Sith magic , an enormous supernova was on a direct course for the Jedi library world of Ossus . With the knowledge that the Sith - created supernova would force the Jedi to evacuate Ossus , the Sith Lords Exar Kun and Ulic Qel - Droma led an attack against the Jedi planet , intent on capturing the vast amount of Force knowledge and tomes that had been collected there over the millennia . Armed with a number of Mandalorian warriors , as well as their army of Krath soldiers , Qel - Droma and Kun stormed Ossus , taking advantage of the confusion and chaos surrounding the devastation headed for the planet . Following their initial invasion , both Sith Lords were involved with various skirmishes , until Ulic was confronted by his brother Cay , who was attempting to turn Ulic back to the light side . The two brothers eventually battled , and the resulting fight saw the death of Cay Qel - Droma at the hands of Ulic . Nomi Sunrider , devastated by having witnessed the death of Cay , managed to use her powers to strip Ulic from the Force . Finally realizing how he had allowed the dark side to manipulate him , Ulic repented and offered to lead the Jedi to Kun ' s hidden fortress on the jungle moon of Yavin 4 . Prelude . During the Battle of Kemplex IX , a sabotaged ancient Sith device used to manipulate matter within the cores of stars caused the detonation of the nearby Cron Cluster stellar group , triggering a massive supernova shockwave in whose direct path lay the Jedi scholar world of Ossus . A large - scale planetary evacuation was called , with military , civilian , and Jedi personnel alike struggling to escape the planet before the nova - wave arrived . The Jedi Masters planet - side began a rescue operation focused upon salvaging as many relics , manuscripts , and other antiquities as possible from the enclave while there still was time . This would , in part , prove to be too tempting an opportunity for Exar Kun to pass up . Linking up with fellow Sith Lord Ulic Qel - Droma and reinforcements of Mandalorian and Massassi warriors , and redirecting Lord Mandalore the Indomitable ' s main battle group to Onderon , Kun launched a raid upon Ossus itself , intent on capturing the vast quantities of Jedi knowledge stored there . The battle . With the evacuation already reaching critical levels , the Sith and Mandalorian ships converged upon the planet , targeting numerous civilian and military transport craft and engaging the Jedi defenses long enough for Kun to slip beneath the screens and land in the enclave . Among his first targets of choice was the residence of Master Ood Bnar , himself attempting to preserve a cache of antique Jedi lightsabers from the oncoming destruction . Engaging Kun and his Massassi , Master Bnar realized that his true skills lay not in combat , but in the powers of the Force . Drawing upon it , the Neti Jedi Master sealed the cache , metamorphosing into a great tree and thwarting the incredulous Dark Lord . He would remain planted there until awakened during Luke Skywalker and Kam Solusar ' s mission to Ossus in 10 ABY . Not far afield , the Cathar Jedi Sylvar assaulted Kun near his ship , seeking revenge for her mate Crado ' s death at Kemplex IX , but was beaten by his elite Massassi guard . Meanwhile , Cay Qel - Droma sensed his brother Ulic ' s presence amongst the battling orbital and sub - orbital ships , and took the " Nebulon Ranger " to the skies in an effort to sway Ulic back to the light . Shot down by Mandalorian ships during the melée , Cay was forced to crash - land in the city , where the two brothers confronted each other for the very last time . Attempting to reason with him , Cay only succeeded in provoking Ulic ' s temper — the dark side surging within him , Ulic instigated a violent lightsaber duel , shearing off his younger brother ' s mechanical arm . Pleading with him , Cay tried to reach through to the Jedi deep beneath Ulic … but in one final surge of anger , Ulic slew his brother where he knelt . Aftermath . As a final act of punishment and retribution , Nomi Sunrider imprisoned Ulic beneath a wall of light side Force - energy . Ulic was forever cut off from the Force and captured by the Republic , thereby becoming the last casualty of the battle . The stage would now be set for the final showdown with Exar Kun at Yavin IV . Behind the scenes . The Battle of Ossus first appeared in the issue " " of the " " series of comics . The battle was conceived and written by author Kevin J . Anderson , and was drawn by artist Dario Carrasco , Jr . The cover art for " Brother Against Brother " , which featured a dueling Ulic and Cay Qel - Droma , was created by Hugh Fleming , a veteran " Tales of the Jedi " artist . Anderson used the Battle of Ossus to bring an end to Ulic Qel - Droma ' s reign as a Sith Lord , and continue the chain of events , begun during the writing of the Battle of Kemplex IX , which would see the fall of Exar Kun and the end of the Great Sith War .