Heartless are the darkness in hearts of living beings given shape and form. They have a thirst for hearts, and are most attracted to pure hearts, such as Sora's. Their existence became known after one was created by Ansem, as revealed by his reports. Emblem Heartless were later created by Xehanort. They first appear in Kingdom Hearts.
Origin
Though the origin of the Heartless is not explicitly described or shown, there was one point where there was not a single person with darkness in their heart, and only light existed, and as such all the worlds were connected. However, people began to grow selfish over the light, and thus darkness was born in their hearts. This darkness eventually consumed the light, but the children of light were able to craft new worlds, though they would remain separate. However, the greatest light would reside in the darkness, and until the day comes when that light breaks through the darkness, darkness would continue to thrive.
An unknown, but large, amount of time later Ansem the Wise, the ruler of the Radiant Garden, discovered the threat of the darkness. In order to combat it, he and his six apprentices, Xehanort, Braig, Dilan, Even, Aeleus, and Ienzo, tried to find a way to prevent the darkness from consuming the world, performing many experiments on the human heart. However, Ansem the Wise began to see the immorality of what he was doing, and ceased his experiments.
But Xehanort and the others continued with their experiments, discovering the Heartless and their nature. They constructed a large factory that could reproduce the creation of Heartless, thus making Emblem Heartless. Thus, the Heartless, once a minor threat, turned into a force that threatened all the worlds.
Heartless Types
Pureblood Heartless are the natural Heartless, born when people's heart are normally consumed by darkness. They are ink-black in color, with yellow beady eyes. They are more common in nature in places that are close to or saturated in darkness. Upon their destruction, they simply disappear in puffs of darkness.
Emblem Heartless, on the other hand, are created from machines that reproduce the process of a heart being consumed by darkness. They have more varied shapes, colors, and are branded with Xehanort's symbol to differentiate them from the Pureblood ones. They mostly appear in the many worlds that reside in the realm of light, unlike natural born Heartless.
Nature
Heartless, Emblem or Pureblood, possess several key characteristics that define them as Heartless. All Heartless are created when the darkness that resides in a person's heart consumes him or her, thus giving the darkness shape and form (this process occasionally forms Nobodies, which are born from the body and soul left behind when the heart is lost). Being born from darkness, they are mindless and master-less, and their only goal is to find hearts, wishing to consume them and consequently create more Heartless. But what they desire above all are the hearts of worlds, and thus they enter worlds in search of the way into the hearts of the worlds. When they consume these colossal hearts, the remains of the world form new worlds, such as Traverse Town and the End of the World.
At the same time, Heartless seek out the users of the Keyblade, since the Keyblades are weapons of light, light being the greatest enemy of the Heartless. In order to stop the users of the Keyblades, the Heartless use the Keyblade itself as a homing beacon, but ultimately desire to take the heart that commands it. Because of this, Keyblade wielders are under constant attack.
Ranking
Heartless, being formed from darkness, have varying strengths, depending on the amount of darkness in a person's heart. And the greater the darkness that forms a Heartless, Emblem or Pureblood, the more powerful and more monstrous it gets. This is a direct contrast to Nobodies, which determine strength by the strength of the will, and the more powerful a Nobody is, the more human it appears.
Control
The Heartless, being mindless, usually have no master to direct their actions. However, there are some higher beings who can command them. But the key to controlling them is an affinity for darkness, and a strong will. Those with hearts, such as Maleficent, endanger themselves however, as the Heartless are attracted to their hearts. If they show weakness, the Heartless will not think twice of consuming their hearts.
On the other hand, higher ranking Heartless, like Xehanort's Heartless, can fully command other Heartless without endangering themselves. Also, Organization XIII is able to command them as well with their strong wills, but are not endangered of being consumed by them for their lack of a heart.
Travel
Heartless make use of the "corridors of darkness", inter-dimensional pathways that connect the many worlds. These pathways are located in the Realm of Darkness, and thus are very dangerous to use if one is not accustomed to the darkness.
Residence
The Heartless reside wherever darkness is abundant, especially the Realm of Darkness. However, they also reside in places such as the End of the World, a collection of the remnants of worlds that is located near the darkness. Another area that the Heartless live in is The World That Never Was, the world of the Nobodies that rests dangerously close to the darkness upon which the Heartless thrive.
Kingdom Hearts
Heartless, as they seek and consume hearts, also desire to return to the greatest heart, the heart of all worlds, Kingdom Hearts, that resides deep within the realm of darkness. And because of this, Heartless seek immense darkness, enough to completely consume the realm of light. The entryway into this place of great power is the Door to Darkness, the door that separates the realm of light and the realm of darkness. However, with the efforts of Sora and the King, the door is closed, which causes the worlds lost to the darkness to be restored, and preventing a massive army of Heartless from pouring into the realm of light.
The forces of the heartless were extremely weakened after the door to Kingdom Hearts was sealed off, though there were still many left. At the end of Kingdom Hearts II, it is unknown what exactly happened to the heartless and if they still pose a threat. It should be noted though that Yen Sid has mentioned that the only true way to destroy all heartless is to have all people have light filled in their hearts and no darkness, leaving nothing to create a heartless or something for them to thrive for.
Types
Pureblood Heartless
- Darkball - Kingdom Hearts
- Darkside - Kingdom Hearts
- Dark Thorn - Kingdom Hearts II
- Gigant Shadow - Kingdom Hearts: Final Mix
- Invisible - Kingdom Hearts
- Neoshadow - Kingdom Hearts (cutscene), Kingdom Hearts: Final Mix
- Possessor - Kingdom Hearts II
- Shadow - Kingdom Hearts
- Shadow Stalker - Kingdom Hearts II
Emblem Heartless
- Aerial Knocker - Kingdom Hearts II
- Aeroplane - Kingdom Hearts II
- Air Champion - Kingdom Hearts II: Final Mix+
- Air Pirate - Kingdom Hearts
- Air Pilot - Kingdom Hearts II
- Air Soldier - Kingdom Hearts
- Air Viking - Kingdom Hearts II: Final Mix+
- Angel Star - Kingdom Hearts
- Ansem - Kingdom Hearts
- Aquatank - Kingdom Hearts
- Arch Behemoth - Kingdom Hearts: Final Mix
- Armored Knight - Kingdom Hearts II
- Artillery - Kingdom Hearts
- Assault Rider - Kingdom Hearts II
- Attachment Tornado - Kingdom Hearts II
- Bandit - Kingdom Hearts
- Barrel Spider - Kingdom Hearts
- Battleship - Kingdom Hearts
- Behemoth - Kingdom Hearts
- Bit Sniper - Kingdom Hearts
- Blizzard Lord - Kingdom Hearts II
- Black Ballade - Kingdom Hearts: Final Mix
- Black Fungus - Kingdom Hearts
- Blue Rhapsody - Kingdom Hearts
- Blue Wyvern - Kingdom Hearts: Final Mix
- Bolt Tower - Kingdom Hearts II
- Bookmaster - Kingdom Hearts II
- Bouncywild - Kingdom Hearts
- Bulky Vendor - Kingdom Hearts II
- Cannon Gun - Kingdom Hearts II
- Chimera - Kingdom Hearts: Final Mix
- Creeper Plant - Kingdom Hearts: Chain of Memories
- Crescendo - Kingdom Hearts: Chain of Memories
- Crimson Jazz - Kingdom Hearts II
- Defender - Kingdom Hearts
- Destroyed Behemoth - Kingdom Hearts: Final Mix
- Devastator - Kingdom Hearts II
- Driller Mole - Kingdom Hearts II
- Emerald Blues - Kingdom Hearts II
- Evil Bumper - Kingdom Hearts II: Final Mix+
- Face - Kingdom Hearts
- Fat Bandit - Kingdom Hearts
- Fiery Globe - Kingdom Hearts II
- Fortuneteller - Kingdom Hearts II
- Gargoyle - Kingdom Hearts
- Gargoyle Knight - Kingdom Hearts II
- Gargoyle Warrior - Kingdom Hearts II
- Grand Ghost - Kingdom Hearts: Final Mix
- Graveyard - Kingdom Hearts II
- Green Requiem - Kingdom Hearts
- Groundshaker - Kingdom Hearts II
- Grim Reaper - Kingdom Hearts II
- Guard Armor - Kingdom Hearts
- Guardian - Kingdom Hearts
- Hammer Frame - Kingdom Hearts II
- Hook Bat - Kingdom Hearts II
- Hot Rod - Kingdom Hearts II
- Icy Cube - Kingdom Hearts II
- Illuminator - Kingdom Hearts II
- Iron Hammer - Kingdom Hearts II: Final Mix+
- Jet Balloon - Kingdom Hearts: Final Mix
- Kurt Zisa - Kingdom Hearts (US/EU), Kingdom Hearts: Final Mix (Japan)
- Large Body - Kingdom Hearts
- Lance Soldier - Kingdom Hearts II
- Lance Warrior - Kingdom Hearts II: Final Mix+
- Living Bone - Kingdom Hearts II
- Luna Bandit - Kingdom Hearts II
- Magic Ghost - Kingdom Hearts II: Final Mix+
- Magnum Loader - Kingdom Hearts II
- Main Core - Kingdom Hearts
- Missilediver - Kingdom Hearts: Final Mix
- Minute Bomb - Kingdom Hearts II
- Morning Star - Kingdom Hearts II
- Neoshadow - Kingdom Hearts II
- Nightwalker - Kingdom Hearts II
- Opposite Armor - Kingdom Hearts
- Organization XIII Mushrooms - Kingdom Hearts II: Final Mix+
- Parasite Cage - Kingdom Hearts
- Perplex - Kingdom Hearts II: Final Mix+
- Phantom - Kingdom Hearts
- Pink Agaricus - Kingdom Hearts: Final Mix
- Pirate - Kingdom Hearts
- Pot Centipede - Kingdom Hearts
- Pot Scorpion - Kingdom Hearts: Final Mix
- Pot Spider - Kingdom Hearts
- Powerwild - Kingdom Hearts
- Prison Keeper - Kingdom Hearts II
- Rabid Dog - Kingdom Hearts II
- Rare Truffle - Kingdom Hearts
- Rapid Thruster - Kingdom Hearts II
- Reckless - Kingdom Hearts II: Final Mix+
- Red Armor - Kingdom Hearts: Final Mix
- Red Nocturne - Kingdom Hearts
- Room Core - Kingdom Hearts
- Rune Master - Kingdom Hearts II: Final Mix+
- Screwdiver - Kingdom Hearts
- Sea Neon - Kingdom Hearts
- Search Ghost - Kingdom Hearts
- Shaman - Kingdom Hearts II
- Sheltering Zone - Kingdom Hearts
- Silent Launcher - Kingdom Hearts II: Final Mix+
- Silver Rock - Kingdom Hearts II
- Sneak Army - Kingdom Hearts: Final Mix
- Sniperwild - Kingdom Hearts: Final Mix
- Soldier - Kingdom Hearts
- Spring Metal - Kingdom Hearts II: Final Mix+
- Stealth Sneak - Kingdom Hearts
- Stealth Soldier - Kingdom Hearts: Final Mix
- Storm Rider - Kingdom Hearts II
- Strafer - Kingdom Hearts II
- Surveillance Robot - Kingdom Hearts II
- Tamer - Kingdom Hearts II: Final Mix+
- Thresholder - Kingdom Hearts II
- Tornado Step - Kingdom Hearts: Chain of Memories
- Toy Soldier - Kingdom Hearts II
- Trick Ghost - Kingdom Hearts II
- Trickmaster - Kingdom Hearts
- Volcanic Lord - Kingdom Hearts II
- White Mushroom - Kingdom Hearts
- Wight Knight - Kingdom Hearts
- Wizard - Kingdom Hearts
- World of Chaos - Kingdom Hearts
- Wyvern - Kingdom Hearts
- Yellow Opera - Kingdom Hearts
Other
- Anti-Sora - Kingdom Hearts
- AntiForm - Kingdom Hearts II (Playable KHII and KHII FM+)
- Data-AntiForm - Kingdom Hearts II (Playable KHII and KHII FM+)
- Retro-AntiForm - Kingdom Hearts II (Playable KHII and KHII FM+)
- Santa-AntiForm - Kingdom Hearts II: Final Mix+ (Playable KHII FM+)
- Vampire-AntiForm - Kingdom Hearts II (Playable KHII and KHII FM+)
- Scar's Ghost - Kingdom Hearts II
- Shadow Sora - Kingdom Hearts