[FairyKing]

I have this theory that each Greeed represents a different kind of desire and feeling of emptiness:

Ankh is the desire for your life to have some kind of meaning (existential angst), because of his wanting to become complete and become closer to human.

Kazari is the desire to take what someone else has (jealousy) because his Yummies inhabited their hosts and because he betrayed the other Greeed and stole medals from them.

Uva is the desire to grow and to increase your wealth and power (ambition) because his Yummies consume what they desire and molt into stronger forms and because he devised a new way of making monsters more cheaply with the Waste Yummies.

Gamel is the desire for worldly pleasures (hedonism) because his Yummies are just created for his childish amusement and because he never thought beyond very simple wants.

Mezool is the desire for other people to care about you (loneliness) because her Yummies spawned in large groups and because of her motherly relationship to Gamel.

And Dr. Maki and the Eiji Greeed represent the desire for destruction and nothingness (death drive) because their power comes from the absence of desire and they have the ability to destroy other medals.