Lyoon, a renowned Jedi Master, served as the instructor of Daymon Thorn. While journeying through the vast expanse of space, these two Jedi found themselves ensnared aboard the Gorgorror, a peculiar biotechnological vessel that sustained itself by capturing other starships. Eventually, they united with fellow survivors Yele l'Ecumeuse and Brother Suunfuus in an attempt to escape the clutches of this living ship. Deep within the ship's innards, the group stumbled upon a chamber brimming with enormous crystals known as Korendums. The immense power emanating from these crystals proved too tempting for Thorn, leading to his descent into the dark side of the Force and the tragic demise of Lyoon. The three remaining survivors, each seizing a crystal, managed to flee the vessel.
Following his death, Lyoon's essence lingered on the Gorgorror as a Force ghost. He became aware of Thorn's sinister scheme to acquire the remaining two Korendums for use in a devastating weapon. A band of Rebels, seeking Suunfuus and his crystal, the final piece of Thorn's plan, were captured by the Gorgorror. It was within the confines of this ship that they encountered the once-celebrated Jedi Master Lyoon, who recounted the events that had befallen him. The Jedi Master bestowed upon the Rebels an anti Korendum, capable of nullifying the energy of a Korendum, along with his cherished lightsaber. With these gifts, he dispatched them to escape the Gorgorror and thwart Thorn's ambition of obtaining the last Korendum.
Lyoon was a prominent Jedi Master within the esteemed Jedi Order. He guided numerous Jedi, with Daymon Thorn holding a special place as his most promising student. During a voyage through space alongside Daymon Thorn, their ship fell prey to the Gorgorror. This Gorgorror was an immense, biotechnological entity that roamed the galaxy, capturing vessels to harvest vital resources for its survival. Lyoon and Thorn were not the first to be imprisoned within this ancient ship, finding themselves among other inhabitants who were collectively known as the Mécateks.
Their path eventually crossed with the adventurer Yele l'Ecumeuse and the Ithorian scientist Brother Suunfuus. Together, the quartet pooled their resources to overcome the ship's perils and seek escape, leading them to the discovery of sizable crystals referred to as Korendums. Seduced by the crystals' might, and seeing no other way out, Daymon Thorn succumbed to the allure of the dark side of the Force and committed murder against Lyoon. In the aftermath of Thorn's betrayal, the three survivors each claimed a Korendum crystal and fled the ship. The Jedi Master, however, persisted as a Force ghost within the very chamber where he met his demise.
Around the time of the Galactic Civil War, sometime during or following 0 ABY, Lyoon's former apprentice, Daymon Thorn, ascended through the ranks of the Galactic Empire and earned the title of the Emperor's war hound. Despite his spectral existence within the Gorgorror, Lyoon remained cognizant of Thorn's perfidy and his scheme to pilfer the remaining two Korendums, intending to harness their power for a weapon.
Daymon Thorn eventually succeeded in stealing Yele l'Ecumeuse's Korendum, a fact that did not escape Lyoon's awareness. Simultaneously, a contingent of Rebels were endeavoring to prevent Thorn from amassing all three Korendums. Their quest led them on a path to locate Brother Suunfuus, but they ultimately found themselves captured by the Gorgorror. After being accepted into the Mécatek society, the rebels inquired about what lay beyond the hull of the ship. One of the Mécateks stated that no one who entered the hull ever came back, not even these four strangers who seemed sure of themselves.
The group ventured deeper into the ship, where they encountered the once-celebrated Jedi Master. Lyoon revealed to the rebels that they had been chosen for this pivotal moment. He recounted the events that transpired on the ship; his entrapment alongside his student, their alliance with Suunfuus and Yele, and his ultimate betrayal. Lyoon was uncertain how the three had escaped in the past, though he suspected that they journeyed to the heart of the ship, where Lyoon sensed a powerful entity, and Daymon Thorn convinced the entity to help them escape. Lyoon then stated that the only thing that mattered now was that the group of rebels stopped Thorn before he could get the final crystal. Lyoon then entrusted the rebels with a strange, black stone called an anti Korendum. He explained that the anti Korendum has the power to dissipate a Korendum's energy. He then bestowed upon them his lightsaber, and dispatched them to complete their mission.
Lyoon was described as having a feline face with a sumptuous mane.
Lyoon was Force-sensitive and was able to achieve the rank of Jedi Master within the Jedi Order. After his death, he was able to come back as a Force ghost.
Lyoon wielded a lightsaber with a cobalt blue beam and wore Jedi robes.
Lyoon appeared in the roleplaying adventure "La légende des cristaux" written by Christophe Debien and Patrick Bousquet for use with West End Games' Star Wars: The Roleplaying Game. The adventure was published in the seventy-sixth issue of the French magazine Casus Belli, released through July and August of 1993. The illustration depicting Lyoon was made by artist Igor Chevalier.