While the «Father» is ultimately the last enemy boss in Fullmetal Alchemist, all the Homunculus are his close soldiers. Keeping up with the RPG analogy, they are the mid-level boss, if you will. They are the ones that Edward and friends have to go through before facing the «Father».
Homunculus themselves are seven beings that represent seven sins, or traits, of humans. Each represents the particular traits that «Father» has shed from himself in order to make him a perfect, emotion-less being. They are highly important characters to the story, and this is what happened to each of them at the end of the Fullmetal Alchemist.
What is The Difference Between Fullmetal Alchemist & Fullmetal Alchemist: Brotherhood?
When they were pursuing Barry the Butcher, Colonel Mustang and Second Lieutenant Jean Havoc stumble across Lust and begin to fight her. Colonel Mustang triggers a closed-room explosion that can evaporate ordinary people, and yet she simply regenerates out of thin air. Not only that, she even manages to stab both the Colonel and Havoc with her blade-like fingers.
Their big break comes when Lust thinks that she has killed the colonel and leisurely fights against Alphonse Elric and Lt. Hawkeye. That is when Mustang suddenly attacked him from behind. He keeps on blasting her with numerous intense explosions to the point she can no longer regenerate and simply turn to dust.
As a homunculus, Gluttony can eat anything he wants. However, the one characteristic that makes him dangerous is his detection ability. Once he catches a whiff of something, he will be able to find it no matter where it is in the world. That being said, he is not a good fighter, and he always dies multiple times whenever he goes against strong opponents.
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