Chaos

Final Fantasy
Chaos is the final boss in the original Final Fantasy. Chaos is the bestial entity created when Garland, a renegade knight, merges with the powers of the Four Fiends. Garland allies with the Four Fiends (Lich, Fiend of Earth, Marilith, Fiend of Fire, Kraken, Fiend of Water, and Tiamat, Fiend of Wind) and forms a convoluted scheme to remain immortal. The Four Fiends control the power of the natural elements and use their elemental powers to destroy civilization. For a reason not stated, their power base is in the past. Their versions 2000 years ago were stronger than the versions which were sent forward in time.

The scheme involves a time loop. Garland, using the Time Gate inside the Black Orb (located in the Chaos Shrine in the present) is sent back in time by the Four Fiends of the present. Garland, after arriving in the past sends the Four Fiends of the past forward in time (Garland's time of departure was sometime after he is defeated by the Light Warriors at the beginning of the game). Then, when the present arrives, the Four Fiends will send Garland back, causing time to loop over and over.

The mechanics of the time loop are: after arriving 2000 years in the past, when the world reaches the present chronologically, Garland would go back in time again. The world is locked in a 2000 year time loop which causes civilization to collapse worldwide. The time loop can only be broken by killing the true enemy 2000 years in the past. The Light Warriors are fated to defeat Chaos, and after the breaking of the time loop, no Fiends remain in the present and all the struggles of the Light Warriors in the present are erased. Only their final battle against Chaos would be recorded in the legends of the land.

It is not clear how Garland transforms into Chaos, whether he merges with the remnaining power of the newly slain Four Fiends of the past or is created through some other process. The ending text seems to indicate Garland's hatred 'burned for 2000 years', which lures the Four Fiends to him, with 'Chaos was created from those four'. How he becomes immortal is unknown since the simple act of traveling through time would not account for that.

Chaos is a giant light brown bestial figure, with large horns giant claws on his hands and feet, talons, bat wings, and a spiny tail. He has shoulder pads, and skulls for knee pads. He also has a second face, a horned demonic face in his abdomen. Chaos uses the most powerful elemental magic, cures, and powerful elemental attacks, each representing one of the four elements.

Final Fantasy VII
After FFI, Chaos does not reappear in Final Fantasy until the seventh entry in the main series. Chaos is the playable character Vincent Valentine's ultimate limit break, in which Vincent transforms into the monstrous Chaos and fights alongside the other characters. However, the player loses control of Vincent when he becomes Chaos. Vincent's Defense and Magic Defense are doubled while he is Chaos and he uses the attacks Chaos Saber and Satan Slam. Chaos Saber hits all foes with an attack power 2.5 times stronger than Vincent's normal attack and Satan Slam also hits all foes but with an attack power 5.625 times stronger than Vincent's normal attack power, and also has a chance to cause Instant Death. This Chaos resembles a grey gargoyle, similar to a plain version of FFI's Chaos.

Dirge of Cerberus -Final Fantasy VII-
Chaos returns as Vincent's form in the final missions of Dirge of Cerberus. This time, the player is given full control of Chaos. This form allows Vincent to hover briefly, to perform a large combo consisting of various claw swipes and kicks ending with a sphere of energy, to perform a large jump equal to a double jump, and to wield a more threatening variation of the Death Penalty (his final weapon from Final Fantasy VII), which gains power as it collects the souls of the wicked. This time, Chaos looks like a demonic, winged Vincent, wielding the Death Penalty. He looks similar to a combination of FFXI's Diabolos and Dirge of Cerberus's Vincent, being a humanoid, winged demon with a red and black color scheme.

Final Fantasy XII
Chaos first appears as a summon in FFXI, where he is an Esper from the world of Ivalice. The Esper of Wind, he represents the Zodiac sign of Taurus, the Bull. Chaos has two large horns on his head, similar to those of a bull. This Chaos does not resemble a winged demon, but rather a demon squatting in a pot, with two detached arms holding down-pointed swords to his sides. The clan primer describes him as such: Tutelary deity of the sacred crystals fashioned by the gods at the time of the Great Making. Created in opposition to Mitron the Chastiser, scion of light. Upon entering the world of Man, he was enveloped in the turmoil rampant there. Lost, he died and was reborn countless times, a walker of life's wheel, eventually to rage against the gods that had so fated him. By sitting in meditation upon the Uneh Pedestal does he clear heart and mind until all that has order and reason and thought is made as nothing.

Final Fantasy XII: Revenant Wings
Chaos returns, along with most of the FFXII Espers, in Final Fantasy XII: Revenant Wings. He is the Rank III flying type Fire summon. He is Mydia's final summon and appears in Mission 39, Wayward Soul, at The Feol Warren. Chaos is backed up by many other Fire-type Yarhi in the boss battle, including Wyverns. This Chaos retains his FFXII appearance, but is alligned with Fire in Revenant Wings. His description is: Walker of the Wheel who writes his foes' fates in flame.

Final Fantasy Tactics A2: Grimoire of the Rift
Chaos returns in Final Fantasy Tactics A2 as a Scion. He can be summoned by anyone who has the Ring of the Wheel equipped. When summoned, he uses Tornado, inflicting Wind-based damage on all enemies. He retains his FFXII appearance.

Dissidia: Final Fantasy
Chaos is the primary antagonist of Dissidia Final Fantasy. He is the god of discord who opposes Cosmos, the goddess of harmony, both being equal in power. However, Chaos summons villains from other worlds to seize control of the Crystals, tipping the balance of power in his favor and setting the stage for the events of the game.

Moves:

Whirlwind: deals damage equal to 50% of the enemy's max HP, with a cap of 9999 FFXII)

Tornado: Chaos transports to the outer reaches of space. Four swords revolve around him while he gestures with his hands. The swords rise high above Chaos' head and spin closely together, then separate into a square pattern. A colorful, square-shaped crest appears, and each of the swords is driven into a corner of the crest. A light strikes Chaos from the air, and strong, swirling winds begin to blow around him, damaging all foes in range equal to 90% of their max HP, with a cap of 9999 damage (FFXII); deals wind damage to all enemies (FFTA2)

Holy: deals light-elemental damage (FFXII)

Darkga: deals dark damage to enemies within area of effect (FFXII)

Firaga: deals fire damage to enemies within area of effect (FFXII)

Thundaga: deals thunder damage to enemies within area of effect (FFXII)

Blizzaga: deals ice damage to enemies within area of effect (FFXII)

Aeroga: deals wind damage to enemies within area of effect (FFXII)

Scourge: deals non-elemental damage and inflicts Sap (FFXII)

Libra: reveals enemies' HP (FFXII)

Auto-Reflect: magic is reflected back to the caster (FFXII)

Auto-Haste: always has Haste status (FFXII)

Auto-Faith: magic potency is enhanced (FFXII)

Renew: fully restores the HP of all allies in range (FFXII International)

Quadrastrike: Deals damage to one foe with four successive hits (Revenant Wings)

Flare: Deals heavy non-elemental damage to one foe (Revenant Wings)

In Greek mythology, Chaos refers to the primordial void, the nothingness that preceeded existence and from which all existence spawned from. It was said to be a vast expanse filled with air and mist. Chaos was considered one of the primordial gods. Chaos had no manifest form. Chaos was the first thing existing after creation. Chaos spawned, without any mates: Erebos, Nyx, Aether, Hemera (Darkness, Night, Aether/Upper Sky, Day), and the Fates. After Chaos spontaneously came into being Gaia, Eros, and Tartarus. In Late Greek cosmology, Chaos came to refer to a chaotic, unordered mass of material, but this is a misinterpretation of the primordial Hyle (mud) from the Orphic mystery cult's cosmogony. Nonetheless, Chaos can be considered the first state of existence for the universe. As the term got translated into English, it came to been the opposite of Order, disorderly, unpredictable, uncontrolled, unrestrained. Chaos was Greek for "gaping void".