One of the theories that I've found to be particularly interesting is Sigmund Freud's Psychoanalytic Theory, which is the first comprehensive theory of personality. Freud was a little crazy so if the theory seems strange to you that's why.
According to Freud, our personality is structured from our biological pleasure seeking impulses, and the conflicts that our society has against these. Freud believed that our personality is the result of our efforts to gratify these impulses, while at the same time not feeling guilty, or receiving punishment for our actions. The three main components of our personality structure according to Freud, is our Id, ego, and superego.
Our Id is what tells us to immediately do whatever pops into our head. It operates on the pleasure principle. If it helps us out, then do it. The Id doesn't think about the negative effects of your behavior. It is like the little devil hovering over your shoulder telling you to forget your homework and go out and party. A person with a strong Id might be very selfish and remorseless.
The superego is the part of the personality that starts developing around 4 or 5 years of age according to Freud. It is the part of our personality that makes us think about the things were are doing. It is in many ways what we might think of as a conscience. The superego tells us the ideal way that we should act. It is like the angel hovering over your shoulder telling you to stay home because you shouldn't be at the party, and your parents will ground you if they find out you went. (I guess I should listen to this more often.) The superego can provide us with feelings of guilt or also feelings of pride.
The ego, is like me in many ways. The ego is like a mediator in an argument. It listens to both sides of the story, and makes the executive decisions. It operates on the reality principle, and it wants to satis