Tash and Zak Arranda first found Eppon inside an egg-shaped pod on the planet of Kiva. As far as they could tell, he was Human. He was only able say one word: "eppon." Tash interpreted this as the child's name. The child was, in fact, trying to say "weapon."
The Arrandas were surprised when the baby began to mature rapidly, becoming a toddler just as a team from the Alliance arrived on Kiva to search Gog's lab for information on Project Starscream. As Eppon continued to mature quickly, the Alliance soldiers began to vanish one by one. His true nature was only revealed after Zak and Tash encountered Borborygmus Gog, whom they had believed to be dead. Eppon was the final stage of Project Starscream and the culmination of the Project's research. Eppon required food to continue growing. He had actually consumed the Alliance soldiers, absorbing them into his body.
Eppon was a prototype of Gog's Army of Terror, a group of biologically-created weapons that would never die, could change form at will, could read the minds of its victims and use their deepest fears against them, grew stronger with each feeding, and were impervious to the Force; this last ability was never completed, fortunately. They would follow any order their creator gave them. As Eppon grew, a purple splotch appeared on his forehead and spread to cover his entire body with a scale-like armor. Over time, the fairly Human-like Eppon transformed into a hideous monster. Eppon nearly consumed the Arrandas' uncle, Hoole, before Tash used the Force to help him free himself from Gog's control. Eppon turned on Gog after realizing his fate, but Gog activated the fail-safe mechanism in each of his warriors. A small explosive implanted in Eppon's brain destroyed much of his body.
In a pseudo-cliffhanger, the epilogue of Galaxy of Fear: Army of Terror describes the remains of Eppon's body moving. While this suggests he may have survived his seemingly fatal injuries, it has never been confirmed and in the text is attributed to the wind.
Eppon bears a strong resemblance to the Metaluna mutants from This Island Earth.