Darth Nihl, a male Sith Lord of the Nagai species, was a member of Darth Krayt's Galactic Empire during both the Sith–Imperial War and the Second Imperial Civil War. Nihl, previously a Nagai warlord, was brought into the One Sith by Darth Krayt, who initially appointed him as his Fist, functioning as a military commander. This changed following the death of Krayt's Hand, or enforcer, leading to Nihl's promotion to that position in 130 ABY. One of his earliest assignments involved leading the attack on the Jedi Praxeum on Ossus, where he murdered Jedi Master Kol Skywalker and inflicted a mortal wound upon the Zabrak Master Wolf Sazen. Nihl then went back to Coruscant and took part in Krayt's ascension to the position of Galactic Emperor. During this event, Roan Fel, the former Emperor of the Fel Empire, was presumed dead, though he actually survived.
For the subsequent seven years, Nihl served as Krayt's primary enforcer throughout the galaxy, until the Dark Lord elevated another individual, Darth Talon, to share the role of Hand. Talon was tasked with capturing Fel's daughter, Marasiah, while Nihl was dispatched to support her during the confrontation on Vendaxa, which involved the Sith, Fel, Imperial Knights, and their Jedi allies. Among those aiding Fel was Skywalker's son, the bounty hunter Cade, who confronted Nihl during the battle on Vendaxa, seeking vengeance for his father's death. Although Nihl did not defeat Skywalker at that time, he later captured the bounty hunter when Skywalker infiltrated the Temple of the Sith in an attempt to rescue the Bothan Jedi Knight Hosk Trey'lis. While Krayt was trying to convert Skywalker to the dark side of the Force, Nihl expressed misgivings about Krayt's decisions, particularly his obsession with Skywalker. Skywalker eventually escaped, and the Emperor's Hand was ordered to defeat him in combat. Nihl was defeated in a duel, losing his right arm chopped off as Skywalker fled. Consequently, he was stripped of his Hand title due to his failure to overcome Skywalker and was placed under the supervision of Darth Maladi for experimentation using Yuuzhan Vong biots.
Later, Darth Nihl was summoned to the planet Wayland by Maladi, where they discussed the state of the One Sith Order following Darth Krayt's defeat during the battle on Had Abbadon. At Maladi's suggestion, Nihl departed for Korriban to uncover the truth about Darth Krayt's demise, a matter he was uncertain about. Upon arriving on Korriban, Nihl, along with Darth Talon, entered the Sith temple's Stasis Room, where Krayt was supposedly resting, only to discover Krayt's empty armor. This left them significantly intrigued about the Dark Lord of the Sith's whereabouts. Nihl promptly contacted Darth Wyyrlok to inform him that Lord Krayt's body was missing and later accompanied the Chagrian when he arrived to investigate. Wyyrlok and Nihl, claiming that Krayt must have been murdered by a member of the One Sith, conspired to keep Krayt's apparent demise a secret. With Wyyrlok assuming leadership of the Sith, Nihl became his primary advisor and was tasked with finding the missing Darth Talon, whom Wyyrlok suspected of being responsible for whatever happened to Darth Krayt. His search led him to Korriban, where he found and fought Talon within the ancient Sith tombs. A resurrected Darth Krayt then revealed himself, unveiling his plan to crush the rebellion to both Nihl and Talon. The two joined the Dark Lord as he stormed Coruscant to confront the usurper Darth Wyyrlok. During the confrontation, Nihl killed several Sith loyal to Wyyrlok, while Darth Krayt himself dispatched Wyyrlok. Subsequently, Nihl was put in charge of a unit of the Dark Lord's elite Sith troopers as Imperial forces prepared to besiege the hidden Jedi Temple on Taivas. When the Dark Lord's trap was sprung, Nihl deployed the troopers, who indiscriminately attacked both allies and enemies as they descended upon the planet. The Nagai later commanded the Sith troopers in a counterattack against the allied force's ambuscade of Coruscant. However, Darth Krayt was killed in battle against Cade Skywalker, leading Darth Nihl to order the execution of all of Krayt's troopers. Following the enemy's victory, Nihl retreated to a secret location and instructed the surviving members of the defeated One Sith to go into hiding with a new objective: to destroy their enemies from within.
Darth Nihl, a male Nagai hailing from the planet Nagi in the Unknown Regions, began his career as a warlord on his homeworld. There, he harnessed his latent Force abilities to lead groups of raiders in attacks across the planet. Darth Krayt, who was in the process of rebuilding the Sith Order, discovered him and offered him a position within the One Sith. Nihl accepted and underwent training to become a Sith Lord. After his initial experience with the Embrace of Pain, his rage and agony drove him to massacre an entire village. He became known as Krayt's top enforcer in Krayt's Sith Order, serving the Dark Lord as his Fist, or military commander. Around 130 ABY, Darth Krayt promoted Nihl to the position of Hand following the death of his predecessor during the war. In this conflict, the Sith allied with the Fel Empire to overthrow the existing galactic government, the Galactic Alliance.

Two standard days after the Empire seized Coruscant, the Galactic Alliance's capital, Nihl led the Sith in an attack on the Jedi Temple on Ossus. He was under orders from Krayt to eliminate all Jedi. However, while carrying out his Lord's directive, Nihl and his forces of Sith and stormtroopers were confronted by Kol Skywalker, a Jedi Master from the New Jedi Order, who sought to provide a group of Padawans with an opportunity to escape Ossus. Although Skywalker and his former Padawan, Zabrak Wolf Sazen, initially achieved some success against the Sith, their efforts proved futile. Nihl engaged Sazen in combat, using his long-handle lightsaber to defeat the Jedi Master. Sazen's weapon arm was severed, and he was subsequently impaled by the Sith Lord, resulting in a mortal wound. After Sazen's defeat, Skywalker directly engaged Nihl in combat, injuring him in a desperate attempt to hold his ground.
Skywalker's son, Cade, soon arrived to aid his father, who had momentarily lost focus during his duel with Nihl. The elder Skywalker instructed Cade to take the wounded Sazen to the Jedi's escape shuttle, preventing Nihl from killing the injured Master. Skywalker continued his stand against Nihl and his Sith, but to no avail; Nihl used his Force lightning to kill the Jedi Master. With the majority of the Jedi on Ossus dead, Nihl left the planet, having achieved victory over the New Jedi Order. He then traveled to Coruscant, where he witnessed Krayt's ascension to Emperor of a newly established Sith Empire by assassinating a decoy of Emperor Roan Fel to seize control of the Fel Empire. Following the decoy's death, the Imperial Moffs pledged their allegiance to Krayt.

Seven years later, Nihl was no longer Krayt's sole Hand. Darth Talon, a Twi'lek Sith, was appointed as Krayt's second Hand and dispatched to Socorro for her first mission: to capture Princess Marasiah Fel and use her to lure her father, the former Emperor Roan Fel, into the open. Talon's goal was to eliminate him and thereby end all resistance to Krayt's complete control over the galaxy. However, Cade Skywalker, who had become a bounty hunting after Nihl killed his father, intervened and prevented Talon from capturing Marasiah. Skywalker, along with his companions, the Zeltron Engineer Deliah Blue and Human co-pilot Jariah Syn, transported Marasiah and her aide, Astraal Vao, to Vendaxa to meet with Vao's brother, Jedi Knight Shado, and Wolf Sazen, the Jedi whom Nihl had presumed dead. Talon attacked them there, albeit unsuccessfully, and requested Nihl's assistance to eliminate the Jedi and capture the princess. Talon instructed Nihl to discreetly deploy troops to her location, await the former Emperor's arrival, and then ambush the Jedi and Imperials to kill them all.
Fel arrived with an escort of two Imperial fighters, which were quickly shot down by the Sith troops positioned by Nihl and his fellow Hand. However, Fel and his accompanying Imperial Knights escaped the destroyed ships only to be confronted by Talon. At that moment, Fel revealed himself to be Imperial Knight Antares Draco. Confused by the deception, Talon was forced to retreat and regroup with Nihl and his troops. He planned to attack the Jedi and Imperials again, hoping to capture Marasiah and kill the others. As they attacked, Nihl once more dueled with Sazen, taunting the Jedi Master with the prospect of killing him a second time. Skywalker, witnessing the Nagai Sith dueling Sazen again and Marasiah mortally wounded by a Zabrak Sith, joined Sazen in combat, seeking to avenge his father. Sazen attempted to stop Skywalker's attack on Nihl, who agreed that Sazen was right to stop Skywalker, stating that wielding a lightsaber did not make him a Jedi. The Sith Lord further mocked him, explaining that vengeance was not a Jedi trait, but Skywalker was not deterred and continued his duel with his father's killer.
As Nihl's duel with Skywalker continued, Sazen was tasked with bringing the princess onto Cade's ship, the Mynock. Nihl, confident that the bounty hunter could not defeat him, offered him a quick death similar to his father's, but Skywalker simply pressed on, wanting nothing less than the Nagai's death. Nihl was subsequently shot by Syn, giving Skywalker enough time to recover, but his companion was soon Force pushed away by Nihl. This left him vulnerable to defeat by Skywalker, who instead escaped with his companions, the Imperials, and Jedi Vao, on the Mynock. Nihl then told Talon that he would soon be the only Hand again, as he believed Krayt would kill Talon for the mission's failure.
Much to Nihl's disappointment, Talon was not killed for her actions on Vendaxa. Instead, a search was initiated for Skywalker, in whom Krayt had an interest due to his potential to heal through the Force. This search proved easier than expected; Skywalker arrived at the Sith Temple on Coruscant to rescue Hosk Trey'lis, a Bothan Jedi Knight whom Skywalker had previously handed over to the Sith for a bounty before having a change of heart. He was attacked by Talon, whom he defeated using the dark side of the Force. Before he could finish her off, Nihl Force choked him, intending to kill the last Skywalker. However, Talon informed Nihl that Skywalker was to be captured alive and that she had been sent to do so. Unable to disobey Krayt's orders, Nihl complied and informed Krayt of Skywalker's capture.

With Skywalker in custody, Krayt hoped to turn the former Jedi to the dark side. By threatening to kill Syn and Blue, the Sith Lord persuaded Skywalker to listen to his offer and consider becoming a Sith. Krayt brought Skywalker to his chambers, but when Nihl attempted to enter, Darth Wyyrlok, Krayt's chief servant, prevented him from entering. Nihl attempted to argue, believing his status as a Hand was sufficient. Wyyrlok did not comply and questioned Nihl's loyalty to Krayt, causing Nihl to back down. Darth Maladi, the head of Sith Intelligence and Assassination, explained to Nihl why he was not allowed entry: Nihl was not born a Sith. Krayt had intended for Nihl to become his Sith military leader, only promoting him to Hand because Talon had not been ready at the time of his predecessor's death. When Nihl questioned Maladi as to why she was not allowed to enter even though she was born Sith, she stated her complete loyalty to Krayt. However, both she and Nihl wondered at Krayt's fascination with Skywalker.
Krayt's attention to Skywalker paid off, and Skywalker agreed to become a Sith, trained by Talon. As Skywalker fell deeper into the dark side, Krayt became convinced that Skywalker could heal him of the Yuuzhan Vong Yorik-Kul implants that were causing his body to fail. As Skywalker began to realize his power under the training of Krayt and Talon, the Sith Lord became obsessed with Skywalker and his potential ability to heal him. Nihl disagreed with this obsession and told Maladi about it. She began to wonder if Skywalker could heal Krayt and what would happen if he died. Nihl firmly believed in the old ways of the Sith; because Krayt had not named an heir, there would be a power struggle. Therefore, Nihl believed that if Krayt could not be healed, Skywalker would be named his heir.
However, Skywalker had other plans; he feigned eagerness to be trained as a Sith and attempted to escape the Temple of the Sith. Talon thwarted this escape attempt, and Skywalker was brought to Krayt to kill Trey'lis, so that he could truly become a Sith. Nihl watched as Krayt ordered him to kill Trey'lis or be killed himself, but Skywalker refused. Krayt attempted to stir Skywalker's hatred of people dying for him as motivation to kill Trey'lis, but the Bothan Jedi intervened, expressing his hope that he would not be used as a weapon of the Sith. For his interference, Krayt struck him down, and a skirmish between Nihl, Talon, Krayt, and Skywalker ensued when the latter had a vision of his father. Using the Force, Skywalker pulled his father's lightsaber toward him, impaling Talon with it, and engaged Nihl in combat.
As Nihl defended himself against Skywalker, Krayt betrayed him, encouraging Nihl's opponent to use his anger and kill the Nagai in vengeance. The duel continued, and eventually Skywalker severed Nihl's arm. Defeated and unconscious, he was then attacked by Skywalker using Force lightning, who intended to kill Nihl as revenge for his father's death. However, at Krayt's beckoning, Skywalker engaged the leader of the Sith in combat instead of killing Nihl. Skywalker was subsequently rescued by his mother, Morrigan Corde, who had allied herself with her son's companions in a plan to rescue the bounty hunter. The plan succeeded, and Skywalker escaped, resulting in the failure of both Nihl and his fellow Hand to keep Skywalker within the Sith's grasp. Krayt was determined to make them both pay for their failure.

Immediately after Skywalker's escape, Maladi and Wyyrlok, along with Talon and Krayt, tended to Nihl. Though the latter was uninjured, Nihl and his fellow Hand were extensively hurt, and Maladi was put in charge of their healing. Since the Nagai's arm was cleanly severed, Maladi offered to reattach it, but Krayt refused; Nihl's incompetence had failed the Sith, and Krayt felt that he was no longer worthy of his arm. Instead, Nihl was to receive a Yuuzhan Vong bioform replacement for his severed limb. Krayt had originally wanted to kill Nihl for his failure, but Wyyrlok convinced him otherwise, explaining that while he could no longer continue as a Hand, Nihl still had use to the Dark Lord. Krayt then replaced Nihl with Darth Stryfe, his Fist, as his new Hand, and sent him and Talon to be healed. Nihl protested his replacement, saying he had earned his place as Krayt's Hand, but Krayt dismissed the complaint. Maladi took the two to her laboratory and placed both Nihl and Talon in bacta tanks.
As his injuries were more severe than Talon's, Nihl continued to heal on Coruscant, while the Twi'lek recovered completely. The former Hand remained in bacta while Lords Krayt, Maladi, Stryfe, and Talon answered the summons of a mysterious female Jedi, who claimed to have Cade Skywalker imprisoned on the Deep Core world of Had Abbadon. Lured into a trap by Skywalker and his colleagues, which included several Imperial Knights, Nihl's fellow Sith were attacked and subsequently defeated. Although Darth Krayt survived the battle, Darth Wyyrlok murdered him shortly afterward, feigning the Dark Lord's survival to all while acting in Krayt's stead as both leader of their Order and ruler of the Empire. Meanwhile, Nihl had fully recovered and had a new arm. He later joined Wyyrlok with several of the more prominent Sith when they returned to Coruscant to secure the Imperial throne in the name of Darth Krayt.

Even though Lord Wyyrlok had successfully misled the majority of the Sith Lords, including Darth Stryfe, and the Moffs into accepting the fiction that Emperor Krayt had survived the assassination attempt and entered a prolonged healing stasis, Darth Maladi, a master of deception herself, harbored serious reservations. On Wayland, Nihl convened with Maladi. She voiced her suspicion that the Chagrian Sith Lord intended to seize control, likely by eliminating anyone he perceived as a threat. Lady Maladi surmised that both she and Nihl, as outsiders not born into the Sith, were likely targets for removal. Further, she asserted that Nihl was a more fitting leader for the Sith and persuaded him to journey to Korriban to verify her suspicions about Krayt's demise and then utilize his findings as he deemed appropriate. Nihl proceeded to the Temple on Korriban, where Darth Talon met him and briefly impeded his progress at the entrance to the Stasis Room. When she denied him access, Nihl fabricated a story, claiming Darth Krayt himself had summoned him. They went into the room together, and Talon was stunned to discover that Lord Krayt's physical body was absent, with only his empty armor remaining – a contingency for which Maladi had prepared Nihl. Soon after, Lord Nihl made contact with Darth Wyyrlok's office through a priority channel. He immediately informed Wyyrlok about Lord Krayt's disappearance.
Shortly thereafter, Wyyrlok arrived on Korriban, and together with Nihl, he scrutinized the stasis chamber where Krayt was supposedly being held. Nihl listened as Wyyrlok declared that someone within the Order must have murdered Krayt and absconded with his corpse. Wyyrlok further stipulated that he and Nihl were obligated to conceal the Dark Lord's death while Wyyrlok governed the Sith until a successor could be chosen; Nihl was designated to serve as Wyyrlok's advisor. Despite his existing knowledge of Krayt's death and the true perpetrator, Nihl swiftly proposed that Darth Talon, his longtime adversary, might be culpable, given her presence in the tomb with Nihl and her subsequent mysterious disappearance. Delighted to have found a scapegoat, the Chagrian concurred and instructed Nihl to locate and interrogate Talon while he returned to Coruscant to manage Imperial affairs. Nihl initiated his search throughout the Valley of the Dark Lords, where he established a bond with a Tuk'ata to aid him in his pursuit.
Nihl located Darth Talon within the tombs of Korriban and, as they engaged in a lightsaber duel, accused her of Darth Krayt's murder. To Nihl's astonishment, Lord Krayt materialized unexpectedly, alive, healthy, and possessing even greater power than before. Krayt reproached Nihl for his ambition and desire to usurp power, but nonetheless spared his life. Alongside Darth Talon, Nihl accompanied Darth Krayt to a hidden chamber where, over the years, he had been amassing an arsenal of Force-sensitive Sith troopers along with new Sith fighters for his new army, an army with which he intended to suppress all opposition and impose peace and order across the galaxy by force.
Around 138 ABY, Nihl went with Darth Krayt as the Dark Lord got ready to retake his throne from the usurper Darth Wyyrlok. They went to Coruscant aboard one of Krayt's newly unveiled Dragon ships and launched an assault on the Sith temple upon their arrival. Darth Nihl, Talon, and two of Krayt's Sith troopers fought through waves of Sith loyal to Darth Wyyrlok as they advanced toward the throne room, where the Chagrian confronted them for battle at the entrance. The onlookers refrained from interfering in the ensuing duel between him and Darth Krayt, and when Krayt emerged victorious, Nihl reclaimed his position by the Dark Lord's side. Shortly thereafter, Lord Krayt discovered the location of the hidden Jedi Temple on Taivas, and prepared his forces for war against his enemies. Darth Nihl received orders to collaborate with the Moffs as the Imperial fleet prepared to assault Taivas, and he was explicitly instructed to keep them in the dark about the existence of Krayt's Sith troopers secretly under his command. During the Sith ambush, the Dark Lord sprung his trap and commanded Nihl to unleash the troopers, a chaotic force that indiscriminately slaughtered everyone in their path—regardless of allegiance—as they stormed the Hidden Temple. Following their victory on Taivas, Nihl and his Sith troopers hurried to join the allied forces in battle for Coruscant.

However, the Sith had underestimated the enemy's strength and determination, and were ultimately defeated on all fronts. In the heart of the Sith Temple, Darth Krayt was killed in combat by the newly-declared Jedi, Cade Skywalker, and death throes rippled through the Force, felt by those attuned to the dark side across the galaxy. Darth Nihl immediately commanded the One Sith to retreat. The Sith troopers, whose lives were intertwined with Darth Krayt's, were driven mad by his death and were ordered to be exterminated by the Nagai Sith Lord. The Sith fleet was destroyed, Korriban was evacuated by any remaining survivors, and Sith forces on battlefronts throughout the galaxy retreated to designated locations to consolidate their remaining power. Nihl was joined by the Inquisitor Darth Havok, to whom he outlined the new strategy for the exiled Sith: a path of patience, cunning, and secrecy; infiltration of galactic governments to undermine the galaxy's foundations, and rebuild it anew.

Darth Nihl began his career as a warlord on his native planet of Nagi before aligning himself with Darth Krayt's new Sith Order. As a member of the One Sith, Nihl faithfully obeyed Krayt's every command, albeit with occasional doubts about the Sith Lord's decisions; for instance, Nihl disagreed with Krayt's fixation on Skywalker, as well as his determination to transform the former Jedi into a Sith. Nihl had studied the ancient Sith doctrines, which stipulated that the most powerful Sith should assume leadership of the Order, rather than a designated heir. Nihl perceived Skywalker as Krayt's intended heir and questioned why Skywalker received privileges denied to him, such as access to Krayt's chambers, despite Nihl's demonstrated loyalty.
Prior to Krayt's obsession with Skywalker, Nihl had taken a personal interest in him. Nihl had murdered his father on Ossus, and Skywalker's desire for revenge against Nihl captured the former bounty hunter's attention. Nihl was also ambitious; he aspired to be the sole Hand and hoped that Krayt would eliminate Darth Talon, his fellow Hand, for her perceived failures. The Nagai was compelled to obey Talon's commands, such as during the confrontation with Fel on Vendaxa and when she prevented Nihl from killing Skywalker, an action Nihl opposed. Darth Maladi later exploited Nihl's ambition to sway him to her side against Darth Wyyrlok, but she underestimated him, as he aligned himself with Wyyrlok when the latter promoted him to secure his loyalty. Nihl exploited his new position to act against his longtime rival, Darth Talon, which was what Maladi feared Wyyrlok would do with her and Nihl since they were not born Sith. Nihl also held the belief that his own abilities as a Sith made him superior to others. He ridiculed Sazen's skill as a Jedi because the Sith had severed his arm with his lightsaber, and he mocked the extent of Skywalker's Jedi training, arguing that wielding a lightsaber did not automatically make him a Jedi.
As a Sith, Darth Nihl possessed fundamental Force abilities, including telekinesis. He employed Force push and pull against Jariah Syn during a confrontation on Vendaxa. Nihl also commanded the Sith power of Force lightning, which he used to assassinate Kol Skywalker on Ossus. These skills, combined with Nihl's proficiency with a long-handle lightsaber, established him as a formidable duelist; he successfully killed a member of the Skywalker lineage, Jedi Master Kol Skywalker, and triumphed over Jedi Master Wolf Sazen in combat. Another ability Nihl employed was Force choke, which he used to subdue and capture Cade Skywalker when he infiltrated the Temple of the Sith. However, Nihl's dueling prowess failed him in a subsequent duel with Skywalker when the latter attempted to escape the Sith temple, resulting in Nihl's defeat and the loss of his arm. Nihl also demonstrated his lightsaber skills in his duel against Darth Talon shortly before the resurrected Darth Krayt's appearance. While pursuing Darth Talon in the Valley of the Dark Lords, Darth Nihl exhibited the capacity to tame a Tuk'ata.

Darth Nihl made his debut in the Legacy series of Star Wars comic books, where he played a significant role as a major character and antagonist in the storyline. Although he was first mentioned briefly in the pre-release issue of Legacy, 0, Nihl appeared frequently in the Broken story arc, in which he murdered Cade Skywalker's father Kol, fueling Cade's desire for revenge and leading him to the dark side. Nihl then made a brief appearance in Allies, playing a minor role, and did not reappear until the next major story arc, Claws of the Dragon, where he captured Skywalker but was defeated during the latter's escape from the Sith. Since then, Nihl appeared in Legacy (2006) 23, and Legacy (2006) 27 that detailed Nihl's replacement as Hand by Darth Stryfe for his failure, and later in the Monster story arc alongside Darth Maladi. Nihl was also mentioned in Lucasfilm official Leland Chee's blog, which revealed that his name is derived from the words "nill, and nihilist." Given Nihl's prominence as a major character during the first nineteen issues of Legacy, he was featured in several sourcebooks, advertisements, and action figures, including The Complete Star Wars Encyclopedia, Jedi vs. Sith: The Essential Guide to the Force, a miniature set for Legacy of the Force, and an advertisement for the miniature set.