While the "Father" is ultimately the last enemy boss in Fullmetal Alchemist, all the Homunculus are his close soldiers. If you follow the RPG analogy, they are the mid-level boss, if you will. They are the ones that Edward and friends must go through before facing the "Father."
The Homunculus themselves are seven beings that represent seven human sins, or traits, of each other. Each represents the particular traits that "Father" has shed from himself in order to make him a perfect, emotion-less being. This is what happened to each of them at the end of the Fullmetal Alchemist.
Colonel Mustang and Second Lieutenant Jean Havoc stumble across Lust and begin to fight her. It''s a closed-room explosion that can drain ordinary people, yet she simply regenerates out of thin air. Not only that, she even stabs both the Colonel and Havoc with her blade-like fingers.
Lust believes 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 continues blasting her with numerous intense explosions to make her feel free to return to dust.
Gluttony is capable of eating anything he wants. However, the one thing that makes him dangerous is his ability to detect something. No matter where the world is, he will be able to find it once he detects something. That being said, he is not a good fighter, and he always dies often when he is facing tough adversaries.
When they encounter the Elric brothers Van Hohenheim, the Chimeras, and Ling Yao, both suffer a lot of damage, but Gluttony is nearing the end of his regenerative limitations. This allows him to utilize Gluttony''s keen sense of smell, but he is also plagued with his imputable hunger.
Envy''s main concern is his shape-shifting ability. That being said, he is often trapped in a situation where he must fight many people. In that situation, Envy will usually resume his true form, which is a huge lizard-like beast with human limbs and faces dangling from everywhere his body.
In the end, Envy chooses to flee his Philosopher Stone and finish his own life, rather than being tipped or killed by the animals he dislikes.
While the capital fight against Envy takes place, a brawl against Sloth is taking place above the ground. Major General Olivier Armstrong of "The Northern Wall of Briggs" is murdered by Sloth, who happens to be with her brother, Major Alex Armstrong, who is formerly known as "The Strong Arm Alchemist."
Both of them manage to handle Sloth at first, but unfortunately, Sloth''s speed and durability proved to be a huge challenge. When the Elric brothers'' teacher, Izumi Curtis, and her husband come to help. Sloth ends up falling on his back, smiling because he can finally rest and dissipate into thin air.
Wrath is actually the Fuhrer of Amestris, King Bradley. Before becoming a homunculus, he was actually a regular human being. A philosopher stone from "Father" imbued into his body transforms him into a super-soldier with enhanced strength, speed, reflexes, and even ultra sharp eyesight. However, unlike his sibling, he age like a regular person.
The final fight for both Captain Buccaneer from Briggs and old man Fu from Xing began at the front of the presidential palace. Both men suffer a bleak injury, but Scar fails to decapitate both of Wrath''s hands until he died due to his many injuries.
Pride is the first homonomculus, and he is a bit tense to fight. His main body is Selim Bradley, King Bradley''s 5-year-old son, but his other form is that of a shadow that can see, talk, eat, cut, and even hold or strangle his opponent.
Pride is severely wounded as a result of having to force Roy Mustang into committing Human Transmutation with him as the medium. That''s why when he confronts Edward Elric, the Fullmetal Alchemist invades his conscience and force his true self out, which is a tiny baby. After that, his body begins to collapse.
Greed is the last Homunculus to leave the earth. Unlike his siblings, Greed has always been following his own wish and not the Father''s Will. After being injected into Ling Yao''s body, he learns to accept humans and even enjoy their company.
Greed has the ability to carbonize his skin, which provides resistance against skepticism. In the final battle against the Father, Greed deliberately attacks him knowing that he will absorb Greed because he requires the Philosopher Stone. Instead of making it stronger, Greed sets forth a knife so that the whole thing falls apart. And that makes the Homunculus come to an end.