Apocalymon

Apocalymon is the one of the ultimate demonic beings in the entire Ultima universe. His very prescence causes a galaxy to end without warning. And the worst part is...he's in Kang's possession. He is also the final antagonist in Digimon Adventure.

Personality
Apocalymon is ultimately jealous of the light. As the beings which composed him were doomed to death by natural evolution, he has to watch as the reverse world, the world of light, get to rejoice in happiness as he suffers. Cursing it, he desires to rule over all the Digimon and the Digital World and twist the world to fit him and his darkness.

In contrast to the English version, the Japanese version (also in the German, Spanish, Brazilian, French and Italian version) has Apocalymon refer to himself in the plural sense. This is likely a reference to the demon Legion, who was also composed of many. Thus Apocalymon, as a being assembled from the data of thousands if not millions of Digimon, may truly have been a plural entity.

Digimon Adventure
Apocalymon's arrival was foreseen in ancient prophecies: he came from beyond the Firewall, and was born from the feelings of jealousy and hatred belonging to Digimon who died during Digivolution. A sadistic and tormented soul, Apocalymon wants to make the Digital and Real worlds into living underworlds to justify the darkness that composes him. His existence generated the chaos in the Digital World, particularly the creation of the Dark Masters and their servants Devimon, Etemon, and Myotismon.

After the DigiDestined defeat Piedmon, the last of the Dark Masters, Spiral Mountain disappears, and the children drop into a strange, empty space. Gennai contacts them, revealing that the true cause of the Digital World's afflictions will soon appear. Apocalymon then shows up, and after demonstrating the techniques of the evil Digimon who compose him, he uses his "Reverse Digivolve" to revert all of the DigiDestined Digimon to their base forms. He then deletes their Tags, Crests, and bodies, sending them all to the Data World.

Once in the Data World, the DigiDestined realize that they have the Crests' power within them all along, and their Digimon are once again able to digivolve. They rematerialize into the Digital World and face off in a battle royale in their highest levels. After Zudomon, Lillymon, MagnaAngemon, Angewomon, MegaKabuterimon and Garudamon destroy all of Apocalymon's claws and distract Apocalymon, WarGreymon and MetalGarurumon destroy his humanoid form. The DigiDestined think that they won; however, as Apocalymon explains, the humanoid form is only a part of him, albeit an important one. He then attempts to take both worlds down with him using his ultimate attack, Total Annihilation. However, the children's Digivices contain the attack, so all that it achieves is his own death. As a result, the Digital World reformats and the time difference between the two worlds equalize.

Video Games
Apocalymon is the boss of two parallel chapters of Digimon Tamers: Digimon Medley: "Saigo no Ankoku Digimon" and "Aratana Sekai", with the minions of his domain the Digimon whose attacks he copies. He has two unique techniques: Shokushu Kougeki and Darkness Zone.

Attacks
 * Darkness Zone (暗黒「ダークネスゾーン」?) : Deletes his opponents.
 * Reverse Digivolve (Death Evolution): Captures the opponent in his claws and forces them to degenerate.
 * Total Annihilation (Gran Death Big Bang): Detonates its own body with enough force to wipe out an entire dimension.
 * Shokushu Kougeki (触手攻撃? lit. "Tentacle Attack") : Performs a physical attack with his tentacle claws.
 * Death Claw: Attacks using his claws.
 * Copied Attacks
 * River of Power (Ultimate Stream): Transforms a claw into MetalSeadramon's head, which fires his River of Power. This technique symbolizes Apocalymon's "Friendship".
 * Crimson Lightning (Bloody Stream): Transforms a claw into Myotismon's upper body, which attacks with his Crimson Lightning. This technique symbolizes Apocalymon's "Love".
 * Giga Cannon (∞ Cannon): Transforms a claw into Machinedramon's upper body, which attacks with his Giga Cannon. This technique symbolizes Apocalymon's "Justice".
 * Death Claw: Transforms a claw into Devimon's arms, which attack with his The Touch of Evil.
 * Virus Grenades (Plug Bomb): Fires Datamon's Virus Grenades from every opening.

Role in Ultima
In Ultima, Apocalymon's data was found by Kang, who reconstituted the demonic monster back into its original form. Sensing the innate possibility of using this villains as a means to take down the Society and Organization at once, Kang has decided to lock Apocalymon within an alternate dimension, and is planning to use him as a very final last resort just in case none of his other methods work. If using Apocalymon to defeat his enemies is the only way he can bring safety and order to the universe...then so be it.