Sigmund Freud is a prominent and debatable figure in modern psychology; he was born in Freiberg, Moravia, in 1856. As the founder of psychoanalysis, Freud is credited for developing new theories on human psychology with special emphasis on the unconscious, dream interpretation, and personality. Freud was born in Moravia, but his family moved to Vienna when he was a child. He was a bright student in school, with early talent in multiple languages and a passion for medicine. He continued his education at the University of Vienna to obtain his medical degree, which he completed in 1881. His first practice as a neurologist evolved to explore human actions and mental illnesses.

Freud's work was influenced by his time with neurologist Jean-Martin Charcot in Paris, during which time he developed an interest in hypnosis and hysteria. After moving back to Vienna, he came up with psychoanalysis, a therapeutic technique that focused on the hidden self. The most important aspect of his theory was that repressed desires and childhood experiences influenced one's behavior and mental state. He devised the idea of the talking cure, where the patient would say whatever came to their mind, allowing the unconscious material to go through. Freud focused on childhood, and, more specifically, in his psychosexual theory, he changed the course of psychology and impacted sociology, literature, and cultural studies.

Among the theories developed by Freud, one can identify such concepts as the Oedipus complex, the structure of the human psyche, the use of defense mechanisms, and others. Nonetheless, Freud's theories were not without controversies, especially those that touched on sexuality and the development of neuroses. His idea that dreams are a manifestation of the wish, published in The Interpretation of Dreams in 1899, was one of Freud's most important works. In time, Freud attracted several faithful disciples, such as Carl Gustav Jung and Alfred Adler, who eventually developed their theories and practices.

In his last years, Freud had cancer due to his cigar smoking and experienced political turmoil. Freud was an Austrian Jewish intellectual who escaped to England in 1938, a year before his death. While some of Freud's concepts, like sexuality and the unconscious, are still hotly contested or criticized in today's psychology, his contribution to the field and his creation of psychoanalysis cannot be denied. He died on September 23, 1939, in London.