Homunculi are artificially created humans. Their origins come from alchemy. In Full Metal Alchemist, when an alchemist attempts human transmutation, they end up losing a physical part of themselves, and while their creation then has life, it is a monster. The most famous homunculi belong to Lady Dante, named after the seven sins. It is also theorized that the heart of a homunculus is the Philosopher's Stone, but this is only a theory.