Chaos

Chaos represents the root of all chaotic things embodied and is the source of all of Dracula's powers. It's the final boss of Castlevania: Aria of Sorrow and it can be considered the de facto main antagonist of the Castlevania series.

Castlevania: Aria of Sorrow
When Soma entered Chaos' room, it chose him to become the next Dark Lord. It stole all of Soma's souls (save for Ability Souls) and fought him in the form of a sphere with three statues on it, each which had a different attack. The red statue would hold all of Soma's Bullet Souls and three easily deflected crystals will shoot out. The blue statue would hold all of Soma's Guardian Souls and would transform into a rushing gargoyle, which could be easily avoided. The yellow statue would hold all of Soma's Enchanted Souls and would summon a targeting reticle to lock on to Soma to steal his MP. Destroying the statues would release the captured souls back to him.

When Soma beat it, it transformed into its true form, a black orb in the middle of the room, which featured black prominences in such a fashion that it resembled a dark sun. It's only weak point was this very core. The core's attacks consist of summoning needles and homing projectiles, all aimed at Soma. A serpent comprised of bones, similar to Death's second form in Harmony of Dissonance, incessantly slithers around the room, dealing massive damage if Soma comes into contact with it. Moreover, four eye-resembling objects are situated in each corner, which occasionally release small black orbs to attack Soma, although these balls can be deflected by attack them. Despite all of Chaos's defenses, Soma felled the eldritch personification of darkness with little difficulty. The Silver Gun is recommended for this final battle, due to it's effectiveness.

When Soma beats Chaos, it shatters. If Soma loses, a cutscene will show a start of a battle between Julius and Soma. Chaos is one of the three enemies in the game that doesn't drop any souls, along with Julius and Graham. Interestingly, Chaos originally had an enemy list entry, which showed a picture of Chaos not used in the game. However, the creators took the entry out of the game, making it unable to get the entry without hacking.

Trivia

 * Each part of Chaos (three colored orbs, eyes, and the black sun) has 3,000 HP.
 * The Black Sun's Defense is reduced for every destroyed eye.
 * In Dracula X Chronicles, during the final battle, when Dracula enters his third form, a large eye in a black void can be seen through a large, cracked hole in the background. It's possible that the eye belongs to Chaos, who may be observing the battle. This is unconfirmed, however.
 * According to the novel Akumajo Dracula: Kabuchi no Tsuisoukyoku, perhaps sometime after Soma had defeated Chaos, the vampire Olrox conquers both the forces of Chaos and humanity.