The Sea Leviathan was a semi-sentient form of Sithspawn, alchemically engineered by the Givin Vul Isen, a scientist in Darth Krayt's One Sith Order. Inspired by the original creation of the exiled Dark Jedi who became the first Sith Lords of millennia past, the Sea Leviathan was born in the depths of the aquatic Outer Rim planet of Dac solely to kill the native Mon Calamari species in accordance with Emperor Krayt's ordered extermination of the entire race. With assistance from the Quarren Sith Lord Darth Azard, Isen summoned the Sea Leviathan from the depths of Dac's Soheras Trench and unleashed it upon the seemingly helpless Mon Calamari, who had been detained in the Imperial Extermination Camp 28.
In 137 ABY, the same year of its creation, the Sea Leviathan met its demise when it was attacked by the Mon Calamari Rangers, led by Imperial Master Treis Sinde. Despite the Leviathan's successful massacre of many Mon Calamari, Sinde was able to coax a school of devilsquid with the Force into an attack on the Leviathan. Unable to defend itself against the assault, the monstrosity was subdued and dragged into the abyss of Devil's Crevasse to be ravaged by the devilsquid.
The Sea Leviathan was an aquatic beast specially bred by the Givin Vul Isen, a scientist of Darth Krayt's One Sith Order, for life in the deep seas of the Outer Rim planet of Dac. It was a creature of considerable length and mass, being of far greater proportions than either the Aquatic Terrain Armored Transport or the Acklay-class mobile fortress, two vehicles used by the military of the Empire. The Sea Leviathan had pectoral fins that were on either side near its chin, as well as a taloned caudal fin for propelling itself through the waters of Dac.
The Sea Leviathan had long tendrils surrounding a gaping maw filled with rows of long teeth. Like its terrestrial cousin, it had two sets of yellow eyes—one atop the other—and four nostrils in a similar arrangement. The Sea Leviathan had a green hide, in contrast to the purplish skin of its land-based kin. Cranial horns were situated on either side of its face and head, which gave way to the rows of blister pods that began at the creature's neck and continued down the length of its entire body. The pods served as siphons of life-energy, as well as being the Sea Leviathan's primary means of attack. Because of special engineering on the part of the beast's creator, the Sea Leviathan only drew upon the energies of the Mon Calamari species; its blister pods were not used to effect any other. Though bred on the planet Dac, the Sea Leviathan was not part of the native fauna. When encountered by the resident Mon Calamari, they recognized it as foreign and regarded the beast with terror before fleeing.
Despite its considerable girth, the Sea Leviathan had incredible speed; it was often able to out-swim its prey and was even able to keep pace with underwater attack craft. Like its land-based relatives, the blister pods with which a Sea Leviathan was equipped were used to siphon life energy from its victims. The beast actively hunted its prey, and when in close proximity, the blister pods resonated with a sickly green aura as they began to drain the life of the intended target. Due to Vul Isen's special engineering, however, the Sea Leviathan only activated its blister pods when hunting Mon Calamari and did not use them when combating other sentient or non-sentient species. Should the beast be attacked by other creatures or beings, it relied only on its size, speed, and teeth as a means of defense.
Sea Leviathans were not a natural occurrence, but were instead a variation of the terrestrial Leviathan that was created through alchemical practices millennia before by the exiled Dark Jedi of the Hundred-Year Darkness. In accordance with Darth Krayt's ordered extermination of the Mon Calamari species, Sith scientist Vul Isen engineered a semi-sentient beast that was not only indulgent upon the life energy of its victims but was also able to assimilate their sentience as well. Each absorbed life allowed the Sea Leviathan to think more like a Mon Calamari; it then instinctively located them in their dwellings and commenced massacring them in kind. The power of the Force was required to bring the beast to life. Through their mastery of the dark side, Vul Isen and his colleague, the Quarren Sith Lord Darth Azard, imprinted parts of their own consciousness onto the Sea Leviathan's mind to awaken it from its vegetative slumber. Once alive, Lord Azard was concerned that as the beast harnessed the sentience of more Mon Calamari, it would turn on the Sith; however, Isen assured him that because their mental imprints were part of the Sea Leviathan's mind, it would ignore them and only hunt its intended prey.
In the year 137 ABY, Dread Lord Darth Krayt ordered that ten percent of the entire Mon Calamari species was to be exterminated for their support and allegiance to the Galactic Federation of Free Alliances, the former dominant galactic government. He commissioned one of his many Sith Lords, the Quarren Darth Azard, as the overseer of his genocidal will. Azard traveled to the Mon Calamari homeworld of Dac, where scientist Vul Isen was also sent and ordered to expedite the success of the Quarren Sith's mission. Lord Azard was content with rounding up the Mon Calamari in detention camps and simply letting them all die of starvation or disease.
Isen, however, had more creative methods of committing genocide and was eager to implement one of his schemes to satisfy Lord Krayt. After consulting the Chagrian Sith sorcerer Darth Wyyrlok, Isen created an aquatic version of the land-based Leviathan to unleash upon the helpless Mon Calamari. Once his oceanic Sithspawn was ready, both he and Darth Azard used the Force to bring the Sea Leviathan out of hibernation from the Soheras Trench and then set it upon a group of Mon Calamari that had been detained in the Imperial Extermination Camp 28. Impressed by the efficiency with which the Leviathan consumed its prey, the two Sith unleashed their handiwork into the waters of Dac as bait for the Mon Calamari Rangers, freedom fighters who had assumed the responsibility of protecting their kinsfolk from the attacking Imperial Sith.
Isen and Azard followed the Sea Leviathan in their AT-AT swimmer to Devil's Crevasse on Dac's ocean floor, where the beast interrupted a reconnaissance mission undertaken by two Mon Calamari Rangers in Krakana underwater fighters. Caught completely unawares, the pair attempted to record as much information as possible about the unrecognized monstrosity before one of the Rangers, Adriphar, created a diversion in order to allow his partner, Shonmai, to escape and report their findings to the remaining Rangers. Though Shonmai successfully got away, Adriphar did not—his Krakana was disabled, and he was killed as his life energy was absorbed by the Sea Leviathan. The creature's presence was exposed when Shonmai arrived back at the Ranger Grotto and alerted her fellow Rangers, who were under the leadership of the Imperial Knight Treis Sinde. While Isen, Azard, and their Sithspawn prowled around Devil's Crevasse, the Rangers devised a plan of attack that involved sacrificing the refugees to the Leviathan while they attempted to disable the Sith's AT-AT swimmer. They met the Sea Leviathan just as it approached the outskirts of the Crevasse, and a battle quickly ensued.
The beast devoured several of the Mon Calamari refugees, while the Rangers, under Sinde's guidance, attacked and disabled the Sith AT-AT. The Sea Leviathan was then mobbed by the Rangers in an attempt to save the remaining refugees, but their flight was halted when the devilsquid—who resided within the Crevasse and had been disturbed by the commotion—appeared. Before the devilsquid could join in the fray and also besiege the refugees, Master Sinde used the Force to command them into action against the Sea Leviathan. Because of its programming to attack the sentient Mon Calamari, the Leviathan did not focus on the squid as they swarmed it. Meanwhile, several of its blister pods were ruptured and destroyed by Sinde, hindering its effectiveness against its desired prey. Unable to withstand the combined assault of the devilsquid, the Mon Calamari Rangers, and the Imperial Knight, the Sea Leviathan was dragged into the abyss of Devil's Crevasse, never to be seen again.
The Sea Leviathan first appeared in the ninth Star Wars: Legacy story arc, Fight Another Day, written by John Ostrander and drawn by Omar Francia. The beast was a take on the land-based Leviathan that was created by writer Kevin J. Anderson for his Jedi Academy: Leviathan comic story arc. The Sea Leviathan was used by Ostrander as a plot device to reintroduce the Genocide of Mon Calamari, an event that first appeared in Legacy (2006) 22, also by Ostrander. To date, the Sea Leviathan's only appearances remain within Fight Another Day.