Sigmund Freud (1856-1939) was a Viennese doctor who came to believe that the way parents dealt with children's basic sexual and aggressive desires would determine how their personalities developed and whether or not they would end up well-adjusted as adults. Freud described children as going through multiple stages of sexual development, which he labeled Oral, Anal, Phallic, Latency, and Genital.
In Freud's view, each stage focused on sexual activity and the pleasure received from a particular area of the body. In the oral phase, children are focused on the pleasures that they receive from sucking and biting with their mouth. In the Anal phase, this focus shifts to the anus as they begin toilet training and attempt to control their bowels. In the Phallic stage, the focus moves to genital stimulation and the sexual identification that comes with having or not having a penis. During this phase, Freud thought that children turn their interest and love toward their parent of the opposite sex and begin to strongly resent the parent of the same sex. He called this idea the Oedipus Complex as it closely mirrored the events of an ancient Greek tragic play in which a king named Oedipus manages to marry his mother and kill his father. The Phallic/Oedipus stage was thought to be followed by a period of Latency during which sexual urges and interest were temporarily nonexistent. Finally, children were thought to enter and remain in a final Genital stage in which adult sexual interests and activities come to dominate.
Another part of Freud's theory focused on identifying the parts of consciousness. Freud thought that all babies are initially dominated by unconscious, instinctual and selfish urges for immediate gratification which he labeled the Id. As babies attempt and fail to get all their whims met, they develop a more realistic appreciation of what is realistic and possible, which Freud called the "Ego". Over time, babies also learn about and come to internalize and represent their parents' values and rules. These internalized rules, which he called the "Super-Ego", are the basis for the the developing child's conscience that struggles with the concepts of right and wrong and works with the Ego to control the immediate gratification urges of the Id.
By today's rigorous scientific standards, Freud's psychosexual theory is not considered to be very accurate. However, it is still important and influential today because it was the first stage development theory that gained real attention, and many other theorists used it as a starting place.