Sigmund Freud 
Three Contributions to the Theory of Sex 

According to Wikipedia: ‘Three Essays on the Theory of Sexuality (German: Drei Abhandlungen zur Sexualtheorie), sometimes titled Three Contributions to the Theory of Sex, is a 1905 work by Sigmund Freud which advanced his theory of sexuality, in particular its relation to childhood… Sigmund Freud (May 6, 1856 – September 23, 1939), was an Austrian neurologist who founded the psychoanalytic school of psychology. Freud is best known for his theories of the unconscious mind and the defense mechanism of repression and for creating the clinical practice of psychoanalysis for treating psychopathology through dialogue between a patient and a psychoanalyst. Freud is also renowned for his redefinition of sexual desire as the primary motivational energy of human life, as well as his therapeutic techniques, including the use of free association, his theory of transference in the therapeutic relationship, and the interpretation of dreams as sources of insight into unconscious desires. He was also an early neurological researcher into cerebral palsy. While many of Freud’s ideas have fallen out of favor or have been modified by Neo-Freudians, and modern advances in the field of psychology have shown flaws in many of his theories, Freud’s work remains important in the history of clinical psychodynamic approaches. In academia, his ideas continue to influence the humanities and some social sciences.’