These Character Bios were written by me.
A homunculus is born everytime an alchemist attempts and fails a human transmutation. Usually unbeknownst to the alchemist, rather than restoring the life they want to restore, another life is born: a homunculus. Although most homunculus look similar to humans(often resembling the human that the alchemist tried to revive), they cannot use alchemy, but they each possess unique and deadly powers, and they cannot be killed by normal methods.
In her attempt to sustain her eternal life and keep the Philosopher's Stone out of human hands, Dante took it upon herself to keep seven homunculus as her servents, feeding them artificial Philosopher's Stones to maintain their form and powers, and making them believe that if they help her get a real Philosopher's Stone, they could use it to become real humans.
Lust was born when Scar's brother went against the laws of Ishbal and used human transmutation to try in vain to revive the woman he loved(Scar was also secretly in love with the woman too.) Lust is able to extend her fingers into long, sharp spears at lighting speed. Probably more than the other homunculus, Lust has a deep longing in her heart to become human, fueled by feelings even she can't truly understand. She's often torn between obeying Dante, and doing what she feels is right in order to follow her own desires. Her feelings become more evident during her encounters with Scar, which seem to bring back some memories of her past life as an Ishbalan woman(she also becomes paralyzed when she sees the pendant the woman used to wear.) After learning of Dante's deceit about the Philosopher's Stone, and realizing that her longing to become human is in vain, Lust decides to help Ed and Al stop the other homunculus. Unfortunately, she's eventually trapped and killed by Wrath.
It's not clear exactly what life Gluttony was born from, but one thing is clear...he likes to eat. He's not big on brain-power at all, but he loves to eat anything, especially human flesh, and his teeth can bite through pretty much any material. He's usually seen in the company of Lust and has a particular liking to her. He became extremely anxious and confused when she was gone, so Dante removed all "attachments" from his mind and made him into a berserk eating-machine. This forced him to eventually return to his original homunculus form(an enormous, multi-appendaged version of his old body.) When Al tried to open the gate to the other world in order to rescue Ed, Gluttony attacked, but Wrath held him off long enough for Al to seal both of them away for good.
Envy was the first homunculus, created when Dante and Hoenheim tried to revive their first son many hundreds of years ago. Although Envy remains loyal to Dante, he(I'm not sure of Envy's gender, but I'm gonna say "he") bears a deep hatred against Hoenheim for running away and marrying Ed and Al's mother. He wants nothing more than to kill Ed in order to appease his anger towards Hoehoeim. Making him one of the trickiest homonculus is his ability to morph into anyone. When Ed sent himself to the other world in order to save Al, Envy was forced to the gate as well, but he chose to enter it in order to finally find and kill Hoenheim once and for all. He turned himself into a giant dragon and willingly flew beyond the gate. He was eventually captured by the people seeking a way to Shambala beyond the gate, and sacrificed along with Hoenheim(killing Hoenheim was the only thing that could calm him), in order to open the gate again.
Although Greed was born from a human transmutation that Dante attempted, he's considered a traitor by the other homunculus because he refused to serve Dante. He was sealed away for over a hundred years in Lab 5, but was revived when Ed set off a large alchemic reaction there. He wanted to use the Philosopher's Stone in order to have immortality, killing whoever gets in his way. He gathered a following of outlaws to help him out and he used the pub Devil's Nest as a headquarters. He's known as a "human shield" because he can change the composition of his body into an unbreakable, indestructible material. Ed was finally able to kill Greed by using his alchemy to change his body's compostion into something he could break though.
Wrath was born when Izumi tried to use alchemy to revive the baby she had lost due to miscarriage. During his journey through the gate, Wrath obtained the right arm and left leg that Ed had given up. He spent many years alone on a deserted island until Ed, Al, and Izumi found him. Izumi tried her best to care for him, perhaps sensing that he was the child she had lost, and Wrath clung to her like a lost child. But Ed was distrustful of him and Wrath's true nature finally came to light when Ed discoverd that not only could he use alchemy without a transmutation circle, but he had his right arm and left leg! Wrath was finally found by Envy, who turned him over to the homunculus side. After that, Wrath went from a scared and lonely child to a wildly aggressive and vengeful homunculus, even using his unique ability to do alchemy in order to kill Lust. However he was still an emotionally unstable and insecure child deep inside; he began to cling to Sloth and call her "mother," and he became completely devastated after she was gone. Finally, after Dante and the rest of the homunculus were gone, Wrath again became depressed and lonely. But he finally did something good by using his powers to sacrifice himself and Gluttony so that Al could open the gate to the other world and rescue Ed.
Sloth was the homonculus born when Ed and Al had attmepted to use alchemy to bring back their mother. She posed as the Fuhrer's secretary, using the name of a deceased state alchemist and changing the military files. The secret of her identity was finally discovered by Hughes, and later Scieszka. She's able to turn her body into liquid, giving her great mobility and defense. Despite being a homunculus, she retains the personality of a caring mother, even towards Ed and Al. But even so, Ed knew she wasn't his real mother and he couldn't let her get the Philosopher's Stone for Dante. So, knowing that homunculus grow weak when exposed to the remains of the person they were born from, Ed dug up the remains of his mother and used it to immobilize Sloth so he could transmute her liquid body and evaporate it.
Pride's origins are unknown, but he's one of Dante's most competent servents. He deceived everyone for quite a while by posing as Fuhrer Bradley of the military. He put on the facade of a gentle and jovial leader, even taking on a wife and son. It was Hughes who first began to find out about the tampered military records. But even after he was killed, eventually more of the homunculus' plot became known, until Al finally discovered that the Fuhrer was really a homunculus! But it was Mustang who had the final confrontation against this powerful homunculus's outrageous speed and evasive abilities. Although he sustained major injuries, Mustang was finally able to defeat the former Fuhrer.