What is the homunculus?

Homunculus refers to the mythological concept of an artificially created human, presumably brought into existence by way of alchemy. 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. 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.