Malachor was a rocky, hellish wasteland planet located in the Chorlian sector of the galaxy's Outer Rim Territories region. It was a planet shrouded in mystery, and the location of an event known as the Great Scourge of Malachor, which took place thousands of years before the rise of the Empire. The Great Scourge was an ancient battle at Malachor's Sith temple between the Sith and the Jedi Order, which saw a superweapon activated, killing and petrifying all the participants of the battle, remaining for years after.
During the reign of the Galactic Empire, Jedi Master Yoda told Ezra Bridger, a Padawan, to find Malachor to help him defeat Darth Vader and the Inquisitors. Bridger, alongside Kanan Jarrus and Ahsoka Tano, traveled to Malachor, where they found the former Sith Lord Maul in exile. Together, they killed three Inquisitors, but Maul blinded Jarrus and escaped, consumed by revenge against the Jedi as well as his Sith Master, Darth Sidious. In the chaos, the Malachor superweapon was nearly re-activated before being destroyed, and while Bridger and Jarrus also fled Malachor, Tano narrowly survived her duel with Vader; years later, Bridger reached through the fabric of space-time to save Tano from Vader's clutches during the duel. With Tano spirited away, Vader departed with his armor scarred by battle, and Tano later returned to the duel's aftermath in order to continue her journey under Malachor's surface with the guidance of Morai.
Malachor was a barren planet in the Outer Rim Territories, located in the Chorlian sector's Malachor system. The planet had a Sith temple located underneath its surface, which resembled an ocean of liquid carbonite that had flash-frozen. Small, pyramidal, solid stone foothills were located equidistant from each other on the surface of the planet. Along Malachor's central latitude was a large crater ringed by narrow spires.
At some point, the Sith were able to establish a presence on the planet Malachor, constructing a massive temple beneath its surface. This temple held a colossal kyber crystal that was used to power the temple. Thousands of years before the brewing war between the First Order and the Resistance, the planet was the location of a massive battle, in which the Jedi Order launched an all-out assault against the Sith. During the battle, the temple's weapon misfired and petrified everyone on the planet. After these events, Malachor was made forbidden to the Jedi, though stories of what had happened were passed down, forming the basis of many legends. Millennia later, the debris of war still littered the battlefield. Any traces of the planet's existence were erased in the Jedi Archives, in the hopes the Sith secrets could be completely lost.
However, many spacers claimed to have found the planet and would bring back Sith relics; some were obvious frauds, but others had genuine connections to the dark side. Smugglers also claimed to make Ashes of Malachor, made from the pulverized bones of those who fought there. These ashes empowered those who consumed it—increasing their might, but at the cost of morality.
Along with the Sith worlds of Jaguada, Rhelg, and Ziost, Malachor was quarantined during the time of the Galactic Republic.
The Sith Lord Darth Sidious traveled to Malachor at one point and experienced a vision of the Sith of lore. At one point, Sidious took the former Nightbrother Maul as his apprentice, the two of them traveled to Malachor. There, Sidious showed Maul a vision of the battle between the Sith and the Jedi. Later, both Sith returned to Malachor, where Sidious showed Maul yet another vision, in which Maul became a Jedi but betrayed those he was helping. Sidious used this to teach Maul that Sith must not act without thinking about their actions. The visions were the result of inhaling the ash of dead Force-users. On another occasion, Sidious visited Malachor and brought back a Sith Chalice.
Due to its infamy, Malachor was often invoked as a curse word. While contemplating his strategy for getting himself and his team of astromech droids off the desert world of Abafar, Colonel Meebur Gascon exclaimed that there was "no way in Malachor" that he would lead his team on an assault on a Separatist landing field. Years later, during the reign of the Galactic Empire, the crime lord Cikatro Vizago of the Broken Horn Syndicate used Malachor as an epithet while working with the smuggler Lando Calrissian.
During their rebellion against the Empire, three rebels—the Jedi Kanan Jarrus and Ezra Bridger, along with Ahsoka Tano, a former Jedi—traveled to the Jedi Temple on Lothal to seek the spectral guidance of Jedi Master Yoda in the hopes of defeating the Sith Lord Darth Vader and his Inquisitors. Yoda told Bridger that, if he and the others wanted to fight, they had to find Malachor. After helping the Phoenix Cell establish a base on Atollon, Jarrus, Bridger, and Tano traveled to Malachor together.
On Malachor, the two Jedi and Tano discovered a deep chasm which led to an ancient Sith temple. There, the three friends were attacked by an Inquisitor known as the Eighth Brother. Bridger was separated and fell into a tunnel. There, he encountered the former Sith Lord Maul, who also wanted to defeat the Sith. Maul befriended Bridger and the two joined forces to venture into the temple in order to find the "secret" that could destroy the Sith. Working together, the two retrieved a Sith holocron from the temple.
Bridger and Maul then reunited with Jarrus and Tano, who were being attacked by the Eighth Brother, the Fifth Brother, and the Seventh Sister. After Maul drove the Inquisitors away, Maul convinced Bridger and the others that they had to enter the Temple in order to activate the holocron. He claimed that doing so would give them the knowledge they needed to destroy the Sith. The Inquisitors soon caught up with them. While Jarrus and Tano fought with the Inquisitors, Maul sent Bridger to bring the holocron to the top of the temple. Meanwhile, Maul killed the Inquisitors before turning on Jarrus and Tano. He blinded Jarrus but was stopped by Tano. While Jarrus pushed Maul off the cliff, Tano went to deal with Bridger. Meanwhile, Bridger planted the holocron into the temple's obelisk. He encountered a female voice who revealed that the temple was an ancient Sith superweapon capable of destroying all life. Bridger refused to use the Temple's knowledge and was attacked by Darth Vader, who had arrived in his TIE Advanced starfighter.
Tano arrived to rescue Bridger and began duel with Vader while Jarrus and Bridger joined forces to remove the holocron. As the temple was building up a power charge, the removal of the holocron caused it to implode. Jarrus and Bridger managed to escape before the temple closed in on them, but they were unable to help Tano, who ensured that her companions escaped before returning to her duel with Vader in the collapsing temple. Tano fought against her former master, refusing to leave him despite Vader's intent to slay his former apprentice.
Jarrus and Bridger were recovered by Chopper, and the three departed the world minus their companion Tano. Maul, who had survived the fall, eventually fled the planet using one of the fallen Inquisitors' TIE Advanced v1s.
As Vader and Tano's duel continued, Vader began to overpower her. As he prepared the fatal blow, Tano was pulled away from the collapsing temple into the World Between Worlds by Bridger and the Force wielder-related convor Morai, surviving the event. Tano was confused how she had departed Malachor and did not know where she was, but Bridger explained to her what had happened. Later, Tano departed the World Between Worlds and returned to Malachor, walking into the Sith temple. Before the convor left the temple, Morai guided Tano through the temple's flooded depths so she could reach another portal to the World Between Worlds.
Meanwhile, a wounded Darth Vader had escaped the temple before it collapsed, limping away from the ruins while being observed by Morai. The Sith Lord would be recovered by an Imperial cruiser.
In Star Wars Legends, Malachor V, as it was known in that era, was a planet that was first referenced in the 2003 video game Star Wars: Knights of the Old Republic. The game revealed that it was the location of the Battle of Malachor V, the final battle between the Galactic Republic, led by Revan, and the Mandalorian Neo-Crusaders during the Mandalorian Wars. The world went on to appear as the final location in the sequel, Star Wars: Knights of the Old Republic II: The Sith Lords, revealing that it was a shattered and ruined world consumed by the energies of the Mass Shadow Generator. This event led to a pyrrhic victory for the Republic, destroying many Mandalorian and even Republic forces in the process. In The Sith Lords, Malachor V housed the Trayus Academy, an ancient Sith academy used by the Sith Triumvirate of Darth Traya, Darth Nihilus, and Darth Sion in the aftermath of the Jedi Civil War. The Jedi Exile, Meetra Surik, traveled to the Trayus Academy, where she defeated Sion and Traya during the game's final levels.
The name Malachor was later used as an expletive by Meebur Gascon in "Missing in Action," an episode of the animated television series Star Wars: The Clone Wars, which, after the 2014 canon reboot, remained in official Star Wars canon.