Sigmund Freud was born in 1856 in Moravia, an area located in the modern-day Czech Republic. When he was just a small boy, his family moved to Vienna, where he grew up, studied, and spent most of his career. Late in life, Sigmund Freud immigrated to England in order to avoid the growing hostilities against Jews in Vienna. He died shortly afterward, in 1939.

Sigmund Freud had his beginnings in medical school. Psychology was in his blood, however, and he was constantly trying to draw a connection between physiology and psychology. In his early years, these efforts were expressed by his adherence to the reductionist theories popular at the time: the attempt to reduce all mental functions to neurology or physiological responses. One might consider his later theories, those that connected virtually everything in human psychology to sexual impulses and instincts, as being along the same lines.

Sigmund Freud is best known for his theory of the unconscious. Freud theorized that the conscious mind – the part of the mind that we are aware of – made up only a minuscule proportion of the mind. Much more important was the unconscious mind, which determines our feelings and actions without us even being aware of it. Although the idea was brand-new, Sigmund Freud succeeded in popularizing it.

Sigmund Freud theorized that many of the psychological problems people face have to deal with memories or experiences that have been repressed by the unconscious. Because we are not even aware of the unconscious, we are unable to deal with what the unconscious has repressed – and unaware of how the repressed memories and experiences are damaging our psychological health. Therefore, Sigmund Freud developed psychoanalysis as a way to deal with the unconscious. He theorized that a mixture of hypnosis and talking about the repressed memories could help the conscious mind come to terms with it, and thereby relieve the patient of his or her psychological difficulties.

Sigmund Freud is also well known for his development theories and their focus on sex. Freud was highly interested in how men and women developed male and female identities. In the most famous part of his stage theory, the Oedipal complex, Sigmund Freud theorized that during early childhood, boys fall in love with their mothers. However, they develop masculine personalities by modeling themselves after their fathers out of fear of castration.

Likewise, Sigmund Freud developed some very famous – and very lingering – theories about women. He theorized that women develop feminine personalities because they believe that they have been castrated; out of what Freud called “penis envy,” they imitate their mothers in order to win a man – and the power his penis represents.