Heartless

The Heartless are the main enemies in the Kingdom Hearts series and are living embodiments of darkness created when a heart is swallowed by Darkness. They reside wherever there is darkness, most prominently the Realm of Darkness. All Heartless act on instinct, seeking out even more hearts to consume and add onto their ranks. Though they have normally been seen controlled by Disney Villains in their appearances, the Heartless will actually ally with whoever is the strongest when two different forces try to control them.

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 act on instinct, their only goal to find hearts, and consume them to 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.

Heartless, being formed from darkness, have varying strengths, depending on the amount of darkness in a person's heart. The darker the heart forming a Heartless, Emblem or Pureblood, the more powerful and more monstrous the resulting being will be. An exception to this is Xehanort's Heartless, who retained his human appearance for unknown reasons. This is a direct contrast to Nobodies, which determine rank according to the strength of the heart, and whose appearances become more human as they increase in power.

The Heartless, being mindless, usually have no master to direct their actions and instead act on the instinct to gather more hearts. However, there are some higher beings who can command them. Heartless will obey those with an affinity for darkness and a strong will. If many people attempt to control them, the Heartless will side with whomever is most powerful. Those with hearts, such as Maleficent, endanger themselves however, as the Heartless are attracted to their hearts and 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.

The primary weapon for destroying the Heartless is the Keyblade, as it is both specially suited for manipulating the bonds between heart, body, and soul which create Heartless, and it is the only object able to thwart the Heartless in their goal of devouring a world's heart. Thus, Heartless seek out users of the Keyblade, since the Keyblades are able to vanquish Heartless very effectively. Because of this, Keyblade wielders are under constant attack. However, in the absence of the Keyblade there are several other options. Magic is effective against the Heartless, as are magical weapons. In either situation, invading Heartless can be made disorganized by defeating the major Heartless which leads them, or the dark heart which attracted them to that world. While this does not by any means purge the world of its Heartless, it gives no small respite from their threat.

Pureblood Heartless
Pureblood are more common in places that are close to or saturated in darkness. Upon their destruction, they simply disappear in puffs of darkness, without a heart leaving its body.

Emblem Heartless
Emblem Heartless were originally created from machines that reproduce the process of a heart being consumed by darkness. Afterward, stolen hearts can become Emblems. Upon gaining more hearts, they become more powerful and multiply. They make up the majority of the Heartless enemies and bosses in both games.

Physical Appearance
Pureblood Heartless are natural Heartless, born from the darkness in people's hearts. They are ink-black in color, with yellow beady eyes. The original type of Heartless, and the most common. They are completely black with piercing yellow eyes and antennas, and have the ability to teleport by sinking into the ground and moving incredibly fast. Sora faces these species many times during his adventures, especially near the end.

Emblem are artifically created Heartless made in the Heartless Manufactory by "Ansem" and Maleficent. They are more common on the worlds within the Realm of Light, and usually mimic the shape of creatures or objects within that world. Unlike the Pureblood, Emblem come in multiple kinds of shapes and sizes, and have various colors with Xehanort's symbol branded on them to differentiate them from the Pureblood ones.

Kingdom Hearts
The Heartless appear to Destiny Islands as the invasion force of Maleficent, intending to consume its heart like the countless worlds that had fallen before the islands. Sora encounters the creatures when Riku opens the door to the heart of the world, causing the Heartless to invade and losing the world in the process. In the midst of the chaos, Sora obtains the Keyblade and is whisked away from the growing darkness in the world. When Sora arrives to Traverse Town, he encounters the Heartless again, but this time he is able to vanquish them with his newly-obtained Keyblade. Joining forces with Donald Duck and Goofy, Sora begins a journey to save the remaining worlds from the Heartless invasion, fighting against Heartless in many shapes and sizes.

Sora eventually learns that the Heartless are being used by Maleficent to capture the seven Princesses of Heart and open the door to Kingdom Hearts, so that she and her allies can rule over all worlds. However, when the group arrives to Hollow Bastion, Ansem, the Heartless' true leader, appears through Riku and reveals that Maleficent and the other villains were being used by the Heartless all along. In order to save the sleeping princesses, Sora then uses Ansem's Keyblade on himself, freeing the princesses' hearts but turning him into a Heartless as a result. Fortunately, Sora is returned to human form by Kairi's light.

After the destruction of Ansem during the former's attempt to open Kingdom Hearts, many Heartless begin emerging from the Door to Darkness. However, their escape is put to a halt when Sora closes and locks the door with the help of Riku and Mickey, who are stuck in the Realm of Darkness.

Kingdom Hearts: Chain of Memories
The Heartless appear inside Castle Oblivion as pawns of Organization XIII.

Kingdom Hearts 358/2 Days
Heartless appear as enemies hunted by Roxas to collect their hearts for the Organization in order to form Kingdom Hearts.

Kingdom Hearts II
Heartless are the generic enemies along with Nobodies in the game. Their reappearance, as Yen Sid explains to Sora, is because although Sora and company prevented a catastrophic invasion of the Realm of Light by Heartless, the Heartless are still a significant threat lingering in the worlds. The Heartless in this edition are important for both Maleficent and the Organization but for different purposes; Maleficent continues to use Heartless to conquer worlds, and Organization XIII uses Sora to release the hearts of every Heartless he destroys to create their own Kingdom Hearts.

Once Sora enters The World That Never Was, Organization XIII's home base, the artificial Kingdom Hearts is damaged when Ansem the Wise fails to encode it as data, causing hearts to rain down over the Dark City, spawning a great swarm of Shadows that swarm the castle while the Nobodies try to catch the falling hearts. Through a temporary alliance, Maleficent and Pete take on the swarm, sending Sora and company to defeat Xemnas, atop the castle. It is unknown what happens afterward, but due to the reappearance of Maleficent in later games, it is assumed that the Heartless were temporarily defeated.

Kingdom Hearts coded
Digital copies of the Heartless appear within the datascape of Jiminy's Journal, just as they had appeared in the real worlds. The digital representation of Sora's Heartless is the source of the datascape's bugs and serves as the game's final boss, but it is defeated by Data Sora and King Mickey, which repairs the journal.

Kingdom Hearts Birth by Sleep
The prequel game reveals that before the Heartless invasion in the first game, Master Xehanort's demonstration the ability to summon Neoshadow to train his apprentice Ventus and Heartless within the Realm of Darkness indicate that the Heartless existed prior to Kingdom Hearts, although only the Pureblood variety was the only appearance of Heartless at the time.

After Aqua's imprisonment in the Realm of Darkness, she encounters several Darksides and decides to let them come at her due to her descent into despair. However, Terra's Keyblade and Ventus's Keyblade apear and destroy the Darksides, giving Aqua hope for escape, and fights her way through the realm and encounters many Pureblood Heartless.

Meanwhile, Xehanort creates the Emblem Heartless within Radiant Garden while experimenting on the heart, which leads to the creation of his Heartless, Ansem, as well as Organization XIII's founding members from the Nobodies of Ansem the Wise's apprentices who begin their plan to harvest the power of Kingdom Hearts. This begins the spread of Heartless to other worlds and become used by each world's respective villain, leading to the events of the first game.