Lust is a Homunculus, nicknamed the “Ultimate Spear”, and one of the first antagonists in the Fullmetal Alchemist series. She is the first Homunculus to appear in the series and plays a significant role in the plot of both the manga and 2003 anime series. Lust is also usually partnered with Gluttony to whom she appears to have a particular almost motherly closeness. Her Ouroboros mark is located on her collarbone, just above her breasts.
-Taken in part from Wikia.
Lust was created by Scar’s brother, when he attempted to use alchemy to bring his lover back from the dead. After he was cast out from Ishbalan society as a heretic, Envy visited the wretched creature and fed it red stones, giving her human shape, and her new name. She was not the first Homunculus to bear the name of Lust, and is the third youngest Homunculus.