Lyoon was a Jedi Master trapped in an ancient ghost ship with his apprentice, Daymon Thorn. After an unknown period of captivity, he found ancient and powerful crystals with Thorn, Yele and an Ithorian scientist. However, Thorn, sensing the power of this treasure, soon fell to the dark side and killed his master before fleeing the Gorgorror.
Lyoon's ghost stayed in the heart of the ghost vessel, waiting for some prophesied adventurers to find him and stop Thorn. When they finally found him during the Rebellion era, he gave to the Rebel operatives an anti-Korendum and his old cobalt-blue lightsaber.
After his death, the Jedi Master was torn between sadness for all the victims of his student and great joy to know that the "champions of the Force" would come one day to stop Thorn.
Lyoon was able to stay in the Gorgorror as a Force ghost. He could also sense fluctuations in the Force over long distances and see the future to some extent. Alive, he was a renowned Jedi Master.
Lyoon was created by Christophe Debien and Patrick Bousquet for the ambiguously canon roleplaying scenario "La Légende des Cristaux," which appeared in the French magazine Casus Belli 76. No picture was provided for him.