Homunculus

Homunculus (Latin for "Little Human", plural Homunculi) refers to the mythological concept of an artificially created human, presumably brought into existence by way of alchemy. Though a common concept, well known and understood by alchemists in Amestris, the idea of homunculi is regarded as no more than a farce or faraway fantasy as no individual or group of alchemists has come anywhere close to successfully creating such a being in officially recorded history. Even so, alchemists have been forbidden by the Amestrian government to attempt or research in the transmutation of humans and State Alchemists have such a restriction as part of their creed.

However, off the official record, not only one, but several of these creatures have been created in arcane, sinister secrecy. In the most relevant sense of the word, "Homunculus" refers to seven individuals who make up the main antagonist group of the Fullmetal Alchemist series. These created humans, named for the seven deadly sins (Pride, Lust, Greed, Envy, Sloth, Gluttony and Wrath), are supernatural beings with incredible longevity, astonishing regenerative properties and a host of varied inhuman abilities. The Homunculi usually carry the mark of the Ouroboros upon their bodies and are identified as such by said mark.

2003 anime
Because of the tangent the 2003 anime took, the origins, identities and secrets of Homunculi differ between the manga and the first television series.

In the 2003 anime, Homunculi are said to be created each time an alchemist attempts a Human Transmutation. While the transmutation itself is a failure in that the person intended to be revived does not return as expected, a new existence is brought about. The result of failed Human Transmutation is a grotesque, vaguely humanoid monstrosity that retains some of the memory, as well as the genetic material, of the resurrected. The "failed" Homunculus generally remains this way until it comes into contact with a Philosopher's Stone. Only then will they reform into an exact replica of the entity that was attempted to be ressurrected. The Homonculi in the first series are notable for being incapable of performing Alchemy

The alchemist known as "Dante" finds these Homunculi and feeds them Red Stones so as to power their growth into full artificial humans, in which state they exist as exact physical duplicates of those upon whom their bodies are based. As a result, they gain supernatural powers and a state of immortality that can only be reversed by presenting the false human with the remains of the original (bone, hair, etcetera). Proximity to these remnants will weaken a Homunculus to the point that he or she can be killed by ordinary methods, in which case the remainder of Red Stones are expelled and the body is destroyed.

Manga
In the manga, the seven Homunculi are the spawn of Father (who himself was the earliest known Homunculus, birthed inside a flask in the ancient country of Xerxes). After having used half the population of Xerxes in the creation of his body, Father himself became a Philosopher's Stone of sorts and became able to siphon off smaller stones from his body to create minions he calls his children. Each Homunculus, as a former part of Father's body and consciousness, is said to have been made up of a different emotional vice - corresponding to their name - and carries that vice as a part of their personality or identity (with Greed being greedy, Pride being prideful, Wrath being malicious and so on).

These Homunculi have physical compositions similar to those of humans but consider themselves superior due to their heightened strengths and abilities. They boast human intelligence and emotions, taking pride in their existence as higher beings, but feeling humility and gratitude toward Father for having given them life. As a result, these Homunculi are largely devoted to the completion of their Father's grand plan. Each of the seven Homunculi has a Philosopher's Stone as its core, fueling its life, regenerative ability and other abilities with a multitude of souls. Each Homunculus can be damaged to the point of death, even to the point of having his or her entire body disintegrated, but can only truly be killed when the Philosopher's Stone heart is either destroyed or runs out of lives to use as power. Envy and Pride have proven capable of absorbing the lives from other Homunculi into themselves to lengthen their lifespans, but it is unknown whether or not this is a trait shared between all seven.

Though the original six Homunculi have bodies that were built around the Philosopher's Stone, for the sake of his plans, Father began experimenting with a new method of Homunculus creation. A new set is created by injecting one of Father's stones into the body of a living human being. The souls in the stone and the soul in the body clash for supremacy, often destroying the body entirely, until one consciousness takes control. Homunculi created in this manner are able to age - a property of which their Stone-based brethren are incapable - and do not give off the "Homunculus' Aura" detectable by certain people.

In chapter 80, it is revealed that the Amestrian government, presumably under the supervision of Father, has created an army of lesser Homunculi whose soulless bodies are stored beneath Central Command. These Homunculi are white, skeletally thin, hairless humanoids with one eye in their foreheads. They lack intelligence and appear only to follow base instincts toward feeding and destruction, similar to the souls within the Philosopher's Stones who have long since forgotten their true identities. Envy, at one point, describes them are mere puppets injected with Philosopher's Stones. They do not regenerate as Father's children do, but are able to keep functioning even if their heads are grievously damaged.

They are awakened in Chapter 90 and disperse over all levels of Central Command, causing incredible havoc. Guns, bladed weapons and even Scar's destruction alchemy are insufficient to kill them.