Apollyon was an ancient Reaper who was exiled to the planet now known as Uke Mochi. After accidentally being unearthed during a mining operation, it attempted to indoctrinate a nearby colony, but was stopped by a team led by Commanders Emmanuelle Sharon and James Fletcher.
Very little is known about Apollyon's history, other than the fact that it predates the Prothean extinction by several centuries. Its life was unremarkable up until sometime in its fifth millenium of life, when it began to believe that the massive amount of resources needed to maintain the already existing Reapers and to build new ones would eventually outstrip the galaxy's resources, leading to a famine. It thus theorized that the Reapers should start exploring the possibility of using smaller forms. To this end, it built an "intelligence core", a smaller form within itself to house its intelligence. When the other Reapers learned of this experiment, they immediately sentenced their fellow Reaper to exile (whether because they regarded its intelligence core as an abomination or because they feared unforseen consequences is unknown.) The Reaper exile's new intelligence core was ripped from its body and buried deep beneath a prehistoric ocean on Uke Mochi. As the eons passed, the ocean receded, and the Reaper exile's oubliette became the bottom of a mine. Eventually, the Protheans created colonies on the planet, which became abandoned when the Protheans were apparently wiped out by the Reapers (who had long since forgotten the Reaper exile's true name, let alone its location.) The Prothean ruins eventually attracted the turians, who attempted to set up a mining operation but were deterred when they discovered the local plants and animals had a right-handed chirality. Meanwhile, the Reaper exile lay far below, biding its time and analyzing its circumstances. That it retained all of the intelligence it had possessed before its exile was evidence of the experiment's success, but now that it was entombed, . Unable to create a new carapece for itself, it instead created "roots" that spread throughout the surrounding area. It used these roots to study the various species that colonized the planet, with the long-term goal of eventually creating husks to gather the resources that would eventually be required to rebuild the parts it had lost. Sometime after the turians abandoned the planet, a "heretical" geth scouting party set up a small base, and Apollyon managed to make contact. It asked the heretics about events that had transpired throughout the galaxy in the years since its exile, but while it gained some useful information, it soon grew irritated when the geth proved to be more interested in genuflection than helping it to escape from its prison. Finally, it convinced them to build it a massive "shrine" deep within the mine's recesses; the final structure was conveniently designed so that it could very easily be turned into a sort of abattoir, and Apollyon cruelly dismantled its erstwhile worshippers and harvested their programs. The entrance to the shrine was then sealed off.
In 2160, the planet was offered to the Systems Alliance as part of the turians' reparations for the First Contact War, and the remains of the turian and Prothean colonies were jointly purchased by ExoGeni Corporation and Ariake Technologies (the latter of which chose the planet's current designation.) By 2186, the humans had begun to explore the mine beneath which the Reaper exile was entombed. One day, while replacing a support pillar, miner Joseph Morita cracked the seal and discovered the shrine. Upon discovering its new prey, Apollyon began indoctrinating Morita, compelling him to close off the entrance with debris and then to sit down in the center of the shrine. Morita stayed down in the shrine for hours, growing weak from hunger and fatigue, until finally the Reaper exile spoke to him and told him that he had been chosen to become the new Messiah and that he must "crucify" himself by inserting intravenous tubes into his wrists and applying electrodes to his scalp. In his weakened state, Morita did as he was commanded, and the Reaper exile used the IV tubes to administer an anaesthetic. It then took parts from the geth that it had dismantled and grafted them onto Morita, turning him into an improvised husk that it dubbed Thamiel (from a Kabbalic reference found in one of the geth programs.)