Sigmund Freud (1856-1939) is known as the Father of Psychoanalysis, a method for treating psychological pathology by means of dialogue between the patient and the psychoanalyst. During psychoanalysis, the patient talks about whatever thoughts come to mind, a process called "free association." The patient is also encouraged to talk about his wishes, fears, and dreams. The role of the analyst is to help the patient gain access to the unconscious conflicts that lie at the root of the psychological problem, and help him gain insight that will lead to resolution.
One of Freud's most important contributions is the idea that the unconscious mind holds the key to understanding conscious thoughts and behavior, and the role that dreams play in unlocking what is hidden or repressed beneath conscious awareness.
Freud is also known for proposing a theory of personality based on the Stages of Psychosexual Development. According to this theory, people gain pleasure from specific erogenous zones as they go through the stages. Freud believed there were 5 stages: Oral, Anal, Phallic, Latent and Genital. At each of these stages, pleasure is focused on a particular part of the body. Too much or too little pleasure in any one of these stages caused a fixation which would lead to personality or psychological disorders. For example, too much pleasure in the phallic stage could lead to obsessive masturbation and sexual dysfunction as an adult.
Freud also developed the model of the psyche composed of the Id, Ego, and Superego. The Id works on the pleasure principle - it seeks to avoid pain and increase pleasure at any cost. It drives us to search for food when hungry, rest when tired, and other basic impulses that ensure our survival. The Superego acts as the moral police, and demands that we act in a moral and socially appropriate manner, no matter the circumstance. It works in direct contradiction to the Id. The Ego works as the executive of the psyche, striving to find a balance between the Id's hedonism and the Superego's moralism.
Although many people find Freud's ideas controversial, he was one of the most influential figures in the entire field of psychology.