Lust

Lust is the leader of the Seven Deadly Sins, a group of artificially made homunculi, and is known to use other people to do her dirty work for her most of the time. She loves nothing more than watching other people fail, but at the same time hates to see her plans crumble. She also has a craving for blood, maybe because she has none of her own.

Even though she seems to be head honcho of the group, she mainly hangs around her loyal parters in crime Gluttony and Envy. The other Sins are as follows: Greed, Pride, Sloth, and Wrath. Edward and Alphonse have met Lust on few occasions, though not formally, really-- she's always on the move, though, and seems to follow them as their journey progresses.

A homunculus is the result of someone attempting to perform a human transmutation (typically a resurrection) and failing. Scar was extremely surprised to encounter Lust, since she bears a striking resemblance to the love of his brother's life. It is known that his brother attempted human transmutation--with disastrous results. Though it's not certain at first, it's assumed that this woman had befallen to some tragedy and that Scar's brother attempted to use human transmutation to bring her back--with Lust as the result. Later, this was confirmed.

Lust is killed by Wrath in the episode "Sealing the Homunculus." In the end of the series, Wrath ends up sacrificing himself so that Al can transmutate the Gate.