A Human male Sith Lord named Tarnis existed during the Great Galactic War and the subsequent Cold War with the Republic, serving the reconstituted Sith Empire. He was the offspring of the famous Darth Angral. Tarnis received training from Lord Praven, his father's apprentice, eventually achieving the rank of Sith Lord. Shortly after the Treaty of Coruscant concluded the Great Galactic War, he began an undercover mission. Adopting the identity of Eli Tarnis, a Republic scientist, he infiltrated the Republic's superweapon programs and quickly rose to lead the design team for the Planet Prison weapon located on Coruscant, the Republic's capital. Although his initial objective was to gather intelligence, Tarnis feared his cover was at risk in 3643 BBY when Jedi Master Bela Kiwiiks arrived to investigate a "dark presence" detected by the Jedi Council. He then initiated a plan to steal the Planet Prison with assistance from the Migrant Merchants' Guild and Black Sun criminal organizations.
After hiring a thief to steal the Planet Prison design files and staging his own kidnapping from the Senate Building, Tarnis escaped to the territory of the paramilitary group, the Justicars' Brigade. However, a young Jedi Knight pursued him. The Jedi Knight, working with the Republic Strategic Information Service, the Coruscant Security Force, and Padawan Kira Carsen, exposed Tarnis's true identity. They tracked the Sith to the ruins of the Jedi Temple, where the Knight and Carsen engaged him in a duel to prevent him from using the Planet Prison against Coruscant. His death, witnessed via hologram by his father, prompted Darth Angral to swear vengeance on the Jedi and begin a crusade for revenge against the Jedi.
Tarnis, a Human male, was born to the Sith Lord Darth Angral either during or before the Great Galactic War against the Galactic Republic. Possessing his father's innate Force-sensitivity, he underwent training under Praven, a pureblooded Sith and one of Darth Angral's Sith apprentices. Tarnis achieved the rank of Sith Lord prior to the Sacking of Coruscant in 3653 BBY, an event where his father's invasion fleet aimed to seize the Republic capital. During this time, Praven joined Darth Malgus and Lord Adraas in the destruction of the Jedi Temple.
When Darth Baras brokered the Treaty of Coruscant, ending the Great Galactic War, Angral was enraged at the missed opportunity to completely defeat the Republic. Tarnis inherited this animosity and was dispatched by Angral to Coruscant as an undercover scientist soon after the treaty's signing. He applied his scientific expertise to General Var Suthra's superweapon projects, a Mon Calamari initiative. Here, Tarnis and other scientists sought to weaponize technologies pioneered by Doctor Nasan Godera during the war. As Doctor "Eli Tarnis," he quickly became the division's chief scientist during the Cold War. While contributing to designs like the Shock Drum and Death Mark laser, his primary focus was the Planet Prison, a weapon designed to ionize a planet's atmosphere, preventing starships from entering or leaving, effectively blockading it without needing additional naval forces. Tarnis also secretly developed a method to combine these weapons into a single device he called the Desolator.
By 3643 BBY, the Planet Prison was nearing the prototype stage. However, Jedi Master Bela Kiwiiks arrived on Coruscant to investigate a dark presence sensed by the Jedi Council. Tarnis, fearing exposure, initiated a plan to seize the Planet Prison and flee Republic territory.
He contacted Black Sun, revealing his true identity to Salarr, its leader. Tarnis offered advanced weapons and armor from the Sith Empire, acquired through the Justicars' Brigade, in exchange for assistance. Black Sun then hired Vistis Garn, a Rodian thief who often worked for the rival Migrant Merchants' Guild, to steal the Republic superweapon design files. Garn and a team raided a military warehouse, acquiring the files and a shipment of heavy weapons.
Roughly thirty hours later, Tarnis was summoned to the Senate Building for a meeting with General Suthra, Jedi Masters Orgus Din and Bela Kiwiiks, and Kiwiiks' apprentice Kira Carsen. Kiwiiks was concerned by Tarnis's apparent indifference to the stolen files, and Tarnis was annoyed by the Jedi's opposition to the Planet Prison. Din's former student then arrived, and General Suthra departed with the two Jedi Masters for a meeting with Supreme Chancellor Dorian Janarus. Agent Galen, a member of the Republic Strategic Information Service, arrived with news that Garn had been identified and tracked to the Old Galactic Market, controlled by the Merchants' Guild.
While Carsen and Galen distracted the criminals using the Coruscant Security Force's network, Din's apprentice, now a Jedi Knight, and the astromech droid T7-O1 went to the Old Galactic Market to retrieve the weapons and plans. As they raided the warehouse where Garn was hiding, Tarnis contacted Black Sun to initiate the next phase of his plan. Exploiting the distraction, Tarnis provided Black Sun with inside information to "kidnap" him from the Senate Building. The plan succeeded, and Tarnis disappeared before security could react.
The Black Sun criminals retreated to the Coruscant Spaceport to create a diversion, while Tarnis took an air taxi to the Justicars' territory rather than the gang's territory, preparing for the next stage. While lieutenant Zeer and his Black Sun forces battled the Coruscant Security Force at Docking Bay 84, Tarnis sent a secure message to the five members of the Planet Prison design team. He convinced them that the Jedi were planning to shut down the project and that the only way to save it was to bring him the prototype in the Justicars' Sector. Believing him, the scientists stole the prototype from their lab and traveled to meet Tarnis at the Justicars' Tower.
Meanwhile, the Knight and Carsen broke through the kidnappers' defenses and learned that Tarnis had been taken to Black Sun Territory. General Suthra discovered that the stolen files contained information on all of the Republic's weapons projects, prompting Masters Din and Kiwiiks and Agent Galen to secure each offworld facility. Galen directed the Knight to the CSF's Special Tactical Unit, and the Jedi and T7-O1 ventured into Black Sun Territory to meet the police officers. The Knight and Sergeant Nidaljo's forces attacked Salarr's headquarters, forcing Salarr to contact Tarnis in a rage. Tarnis dismissed Salarr's accusations and ordered him to kill the Knight, who had just entered the room and overheard the conversation via holocomm. When the Jedi accused him of treason, Tarnis revealed his true identity as a Sith Lord before ending the call to meet with his design team.
The five scientists handed over the prototype to Tarnis, but were horrified when he activated his lightsaber and used lightning to cut them down. Tarnis swiftly eliminated the defenseless scientists, though one man, Jonkan, survived long enough to see the Sith leave with the prototype. Tarnis descended into the industrial sector known as the Works, where Imperial soldiers escorted him to the ruins of the Jedi Temple. He began setting up the Planet Prison in the chambers of the Jedi Council.
Jonkan lived long enough for the Jedi Knight and Carsen to arrive. Before dying, he explained that the device needed time to charge and generated immense heat. Using this information, the two Jedi located the weapon in the Jedi Temple and raced to the ruins, fighting through the Imperials guarding it.
While waiting for the device to charge, Tarnis contacted his father via a secure holotransmission routed through Ord Mantell and other planets, informing Angral and his three apprentices, Sadic, Praven, and Nefarid, of his success. Angral praised his son's accomplishments, but the Knight and Carsen stormed into the room. Sadic mocked Tarnis for leaving loose ends, but Angral urged his son to stop the Jedi. Tarnis refused the Knight's offer of surrender, summoned his red-bladed lightsaber, and unleashed a storm of violet lightning before charging. Despite his skill with the blade and the dark side of the Force, Tarnis was no match for the younger Jedi's martial skill and strength in the Force. Their duel ended when the Knight struck down the Sith Lord before the unbelieving eyes of Tarnis's father.
Tarnis's death drove Angral to the brink of madness, and he declared war on the Republic to avenge his son. Exploiting Tarnis's research on combining superweapon technologies, Angral combined the stolen weapons into the planet-killing Desolator. After successfully testing it on the agriworld Uphrades, Angral attempted to destroy the Jedi Order's homeworld of Tython. However, the Knight was able to defeat Angral aboard his flagship Oppressor, ending the Desolator's threat.
When Praven faced the Knight on Tatooine, he realized that the Jedi's power was responsible for Tarnis's death and was satisfied that his training was not at fault. Tarnis's work on the Planet Prison was later adapted into the Firestorm Turbolasers by Imperial scientists during the Battle of Corellia several years later.
Tarnis, a Human male, had green eyes like his father and brown hair and pale skin in his "Eli Tarnis" persona. However, when he dropped the disguise, the dark side visibly darkened his skin, and he wore a hooded cloak. Tarnis was arrogant and cruel, traits that seeped through his disguise, making him appear stuffy and self-important. As a Sith Lord and Darth Angral's son, he believed himself invincible and fully trusted the dark side to ensure his victory. He discarded allies like Salarr, Black Sun, and his research team once they were no longer needed, confident in his success. His arrogance stemmed from his brilliance and dark side strength, which he used to achieve his objectives.
As Darth Angral's son, Tarnis inherited his father's Force strength and was trained by Praven. In battle, he wielded a red-bladed lightsaber skillfully, but relied more on Force blasts and lightning. His true skills lay in subterfuge, maintaining his cover for nearly a decade, and in science. Tarnis's work significantly advanced the superweapon projects, and he developed a method to combine the Shock Drum, Death Mark laser, and Planet Prison into a single ship-mounted weapon, a feat acknowledged as brilliant even by Nasan Godera.
Tarnis debuted in BioWare's 2011 massively multiplayer online role-playing game, Star Wars: The Old Republic. He serves as the ultimate antagonist of the Coruscant section of the Jedi Knight class Prologue. He is first encountered as "Doctor Eli Tarnis" in the mission "The Jedi Envoy" and is the target of the missions "Kidnapped!," "Rescue," "Tracking Down the Traitor," and "Race to the Ruins," with his identity as a Sith Lord revealed at the end of "Rescue". When the player faces Tarnis in the Jedi Temple, they can choose to ask him to surrender or attack, but they will ultimately fight and kill him.
In the game's 2015 digital expansion, Knights of the Fallen Empire, Tarnis appears in the hallucination scenes of Chapter 2 as an enemy for players, who take the role of the "Outlander," of the Jedi Knight class.