The Leviathans were an ancient species of serpentine creatures that were bioengineered. These creatures were created by Dark Jedi who had fallen from grace during the era known as the Hundred-Year Darkness. While some accounts suggest Karness Muur as their possible creator, Sorzus Syn claimed responsibility for their creation within her chronicle.
Leviathans were massive, meat-eating reptiles designed to serve as mobile superweapons on the battlefield. Their purpose was to siphon the life force of enemy combatants into blister traps located on their broad backs. They hatched as serpentine larvae, lacking limbs, eyes, and the characteristic blister traps. However, even in this early stage, they exhibited aggression towards other living beings. Upon reaching adulthood, Leviathans transformed into large, bipedal beings with four smaller forelimbs and two tentacles surrounding their jaws. The skin of a fully grown Leviathan was incredibly resilient, allowing them to traverse lava without sustaining damage.
During the adult phase, Leviathans also grew numerous blister traps used to contain the life energies of their victims. Upon killing a creature, they would absorb its life force and knowledge. Even if someone was extracted from these blister traps, they would experience rapid aging and weakening. Adult Leviathans also possessed the ability to disrupt the sensory perceptions of Force-sensitives, inducing auditory hallucinations of screams, intense headaches, and obsessive behaviors aimed at alleviating the pain. Mature Leviathans had long tentacles surrounding a large mouth filled with rows of sharp teeth, two pairs of eyes stacked vertically, and four nostrils arranged similarly. They could project fire, contributing to their terrifying reputation. While those on Corbos displayed purple skin, their counterparts on Kesh had bluish-green skin.
Leviathans were capable of entering hibernation for thousands of years, awakening when prey was nearby. They could be killed by sustained attacks with lightsabers. While their immense size gave them an advantage in close combat, they could also be destroyed by concentrated fire from turbolaser cannons and even Force lightning. Like many other lifeforms, Leviathans were also vulnerable to electrocution.
Despite their immense bulk, Leviathans were surprisingly fast and could overtake their prey. They used the blister traps on their backs to drain the life energies of their victims. These beasts actively hunted, and when they ensnared prey with their tendrils, the blister traps would glow with a bright blue light as they extracted life energy and knowledge. Leviathans preyed on a wide variety of species, including Humans, Rodians, Keshiri, S'kytri, and even non-sentient creatures like uvaks. After consuming the life essences of their prey, Leviathans absorbed their knowledge and intelligence, which could be accessed by whoever controlled them. When attacked, Leviathans relied on their size, teeth, and tendrils for defense.
Leviathans possessed the cognitive abilities of a non-sentient animal, despite their size and power. They viewed all other beings as food and were incapable of intelligent speech, instead communicating through grunts and roars. The Dark Jedi Baron Remulus Dreypa used a Sith amulet to command the Leviathans on Kesh. Even without a master, they posed a threat. Some Leviathans on Corbos were known to hibernate for millennia, emerging when they sensed a large number of potential prey.
The species came into existence during the Hundred-Year Darkness, predating the formal establishment of the Lords of the Sith. Therefore, their creation must be attributed to dark-side alchemy discovered independently of established Sith Alchemy practices, thus they are more accurately called "dark-side spawn." However, the term Sithspawn became more widely used throughout history. The Dark Jedi and future Sith priestess Sorzus Syn stated that her work creating Howler, Shambler, Pit Horror creatures eventually culminated in the creation of Leviathans. Her experiments with Leviathans would later help her master and improve Sith Alchemy. One specimen, called Krespuckle the Ever-Hungry, became her personal favorite.
The Exiles primarily created Leviathans to strengthen their armies toward the end of the war. Following the Battle of Corbos in 6900 BBY, Leviathans nearly vanished from the galaxy. A small population survived on Corbos, remaining undetected. These survivors became increasingly feral, emerging only when colonists attempted to settle on the planet. Over the following millennia, numerous groups of colonists were wiped out, with their disappearances remaining a mystery. Meanwhile, these Dark Jedi were exiled by the Jedi Order into the Stygian Caldera where they forged the Sith Empire. The Sith priestess Sorzus Syn also established a laboratory where she grew several Leviathan larvae.
After their exile, the Sith Lord and former Baron Remulus Dreypa, along with some of his fellow exiles, decided to abandon the Sith Empire and seek revenge against the Jedi Order and the Republic. They assembled a strike force, gathering new armies and several Leviathans. These Sith Lords abandoned their less committed brethren and left the Stygian Caldera. However, Dreypa's forces encountered a Jedi patrol composed of Corbos veterans searching for the Exiles to prevent them from retaliating against the Jedi and the Republic. After a chase across the galaxy, the Jedi and Sith ships crashed on Kesh, where the space battle turned into a massive conflict involving lightsabers and Force powers. During the Great Calamity, several Leviathans were released, causing widespread destruction. Many Keshiri natives were killed during the fighting.
However, the Sith became disillusioned and disgusted by the damage they had inflicted on the Keshiri. They imprisoned Dreypa in an oubliette and made peace with the Jedi. Stranded on a remote planet, the two Force orders retreated to the frozen continent of Eshkrene in the south pole, establishing a new community and order known as "The Doomed," which aimed to find balance in the Force. Before his capture, Dreypa had hidden several Leviathan larvae within the volcanic crater at Sessal Spire. These Leviathans remained dormant beneath the volcano until 2974 BBY. After his escape, Dreypa led a peasant uprising against the ruling Lost Tribe of Sith, but his forces were defeated at the Battle of the Marisota Floodplain. Dreypa and his local collaborator Parlan Spinner lured the Tribe's commanders to the volcano, where they unleashed the Leviathans.
The Leviathans quickly decimated much of the Lost Tribe's forces and destroyed an army of "Doomed" adherents who had flown on a flock of uvaks in an attempt to stop Dreypa. During the battle, Spinner betrayed Dreypa and helped save the lives of his former enemies—the Grand Consort Iliana Hilts and her daughter Takara—from being devoured by a Leviathan. He managed to wound and temporarily immobilize the Leviathan grabbing the Grand Consort and her daughter. While Spinner had managed to stop the monster before it could steal her entire life force, Iliana was transformed into an old woman. Dreypa's Leviathans then laid siege to the Lost Tribe's capital at Tahv, causing the city extensive damage.
However, they were stopped by Spinner who had stolen an ancient Jedi starship hidden under the city and he used the ship's tractor beam projector to drag one of the Leviathans before killing it with turbolaser cannons. Spinner then proceeded to destroy most of the remaining Leviathans with the Last Hope's armaments. The last remaining Leviathan was then slain by the Sith princess Takara who nearly beheaded it with Force lightning. Dreypa himself perished at the end of the Siege of Tahv when Spinner locked the starship's autopilot and sent it on a one-way journey into Sessal Spire's volcanic caldera. Spinner and Takara survived the battle and the Lost Tribe rebuilt its damaged capital and consolidated its power over Kesh. The former outcast himself became one of the Grand Lord's Hands which greatly improved his social standing within the tribe.
By the time of the New Republic, most people in the galaxy believed Leviathans to be extinct, although their fearsome reputation persisted. In 12 ABY, the New Republic established a mining colony on Corbos. However, their activities awakened a Leviathan, which attacked the settlement and devoured the workers, draining their life energies. The Corbos miners managed to send a distress transmission to Coruscant. With the Combined Defense Forces of the New Republic occupied with the Imperial warlords, Admiral Ackbar convinced Senator Leia Organa Solo to ask Jedi Master Luke Skywalker to send Jedi students from the new Jedi Praxeum on Yavin 4 to address the Corbos problem.
Master Skywalker dispatched the new Jedi Knight Kyp Durron and Dorsk 82, a clone created to replace the deceased Dorsk 81, as was his planet's custom. Upon arriving, Kyp and Dorsk discovered that the entire Corbos Mining City had been destroyed. Searching through the ruins, they found broken weapons and blood, indicating that the miners had been killed. However, Kyp was disturbed by the fact that he could hear the miners screaming for help through the Force, leading him to believe they were still alive. Upon finding more blood he realized that they must be dead. Kyp then suggested that they sleep in the ruins and search for the creature the next day. However, Kyp was unable to sleep due to the constant screaming and wailing he sensed through the Force. He went alone to find the beast.
When Dorsk 82 woke up and found that Kyp was gone, he contacted the Jedi Academy and requested for reinforcements. Meanwhile, Kyp's trail led him to a steep cliff where he found the fossil of a deceased Leviathan. Kyp continued to sense the screams of the deceased and miners and decided that he must continue to find the source. Back on Yavin IV, Skywalker dispatched two more Jedi—Kirana Ti and Streen—to go and help Kyp and Dorsk on Corbos, having received Dorsk 82's call for help. After climbing another cliff, Kyp finally encountered the Leviathan. After goading the beast, Kyp engaged the Leviathan in a vicious battle and inflicted numerous lightsaber wounds before finally using a grappling hook to climb onto its back. There, he discovered the ghoulish faces of the miners within a milky portal which turned out to be the creature's blister trap. Kyp used his lightsaber to penetrate the blister and free the trapped spirits.
However, the Leviathan flung the Jedi off its back and grabbed Kyp with its tendrils, intending to force him down its maw. Meanwhile Kirana and Streen quickly teamed up with Dorsk 82 to search for Kyp within the mines. They also encountered several Leviathan larvae which they proceeded to kill. Meanwhile, Kyp managed to break free of the Leviathan by unleashing Force lightning which fried the monster. He then released the miners' spirits from the blister traps of the deceased creature. By then, the other Jedi had succeeded in climbing out of the mines and found Kyp standing by the body of the monster. Dorsk 82 gave Kyp his lightsaber back, which he had picked up on the way out. Without warning, a much larger Leviathan appeared and attacked the four Jedi.
After a fierce battle, the Jedi team managed to force the monster into a volcanic crater and, believing it to be dead, stood around the lava. However, Kyp commented that he could still hear the terrible screaming in his head and his words were confirmed as the monster emerged unscathed from the lava. The Jedi continued to fight it, trying to avoid the drops of lava now falling all around them. Eventually Dorsk 82 discovered a functioning power generator and convinced Kyp to attach the cables around the monster in order to electrocute it. Kyp succeeded in entangling the Leviathan within the cables and Dorsk 82 hit the switch. Instantly, the huge monster was engulfed with electricity and was killed.
Following Kyp's mission, several archaeological teams visited the planet in the following years, but they didn't report any Leviathan sightings, supporting the conclusion that the species was extinct. Regardless, colonists and miners continued to avoid the planet under the belief that some of the creatures may have survived underground, even though there was no proof of this.
In 137 ABY, Vul Isen, a scientist working for the One Sith, bioengineered a species of Sea Leviathan to assist in the genocide on the planet Dac. After the Sea Leviathan was destroyed, Treis Sinde informed Roan Fel that the One Sith might attempt to recreate and mass-produce the land-based species as the Second Imperial Civil War continued. However, the failure of the Sea Leviathan and the increasing threat posed by the resurgent Jedi and the Galactic Alliance Remnant led to the abandonment of further Sith plans to create more Leviathans for the war effort.
Rather than allocate more resources to Dac, Darth Wyyrlok, the Sith Regent, instructed Vul Isen to initiate the [Final Protocol]: the eradication of all life on the planet. Pleased with the prospect of continuing his work elsewhere, Isen contaminated Dac's oceans with viral spores, which would be spread by oceanic currents and kill every life form on the planet within a week. Within three days, Dac's oceans were filled with the corpses of the dead. Isen's actions resulted in the deaths of over eighty percent of the planet's population and would have caused complete extermination if not for the intervention of the Galactic Alliance Remnant and a fleet of civilian volunteers.
The Leviathans were initially conceived as a primary antagonist in Kevin J. Anderson's Jedi Academy: Leviathan comic series, which was published from October 1998 to January 1999. In this standalone comic, the Leviathans were drawn by Dario Carrasco, Jr.; inked by Mark G. Heike, Bill Black, and David Jacob Beckett; and colored by Ray Murtaugh. Their origins as Dark Jedi sithspawn were further detailed in other Expanded Universe works, such as Bob Cooper's article Straight from the Horse's Mouth, which appeared in Star Wars Insider 35, and Daniel Wallace and Anderson's The New Essential Chronology, first released on October 25, 2005. The New Essential Chronology connected the Leviathans to the Dark Jedi responsible for the Hundred-Year Darkness. Wallace's Book of Sith: Secrets from the Dark Side, first released on February 10, 2012, identified the Dark Jedi exile Sorzus Syn as the creator of the Leviathans.
Leviathans also appeared briefly in a flashback in John Ostrander and Omar Francia's Star Wars: Legacy series in Legacy (2006) 30, which debuted on November 26, 2008. Leviathans later served as a conceptual basis for the aquatic Sea Leviathan, which debuted in the ninth Legacy story arc, Fight Another Day. This story arc focused on events on the planet Dac and consisted of two issues, published from January 28 to February 29, 2009. Leviathans also appear as minions of the Sith Lord Remulus Dreypa in John Jackson Miller's standalone Star Wars: Lost Tribe of the Sith comic series, which ran from August 8 to December 12, 2012. They first appeared at the end of Lost Tribe of the Sith—Spiral 3, which was released on October 10, 2012. For this standalone comic, the Leviathans were drawn by Andrea Mutti, inked by Pierluigi Baldassini, and colored by Michael Atiyeh.