Humans created by alchemy. Depending on the advancement of a homunculus, they have varying levels of immortality. Ennis is a relatively complete homunculus (she is completely immortal but does not possess complete knowledge of the world). Other homunculi include the Lamia and the children of bottle. The Lamia never age but are vulnerable to wounds.
Theory
Homunculi are supposed to small men inside a flask. They are said to possess knowledge about everything about the world, and that is why their size is so diminuitive.
Homunculi
Szilard Quates's Homunculi
Huey Laforet's Homunculi
Hilton
"The Poet"
Reil
Frank