Sigmund Freud (6 May 1856 – 23 September 1939) was the founder of psychoanalysis. After studying the technique of hypnosis under Charcot, he started treating patients with hypnosis along with Breuer.
Freud developed the therapeutic technique of free association (in which patients report their thoughts without reservation and in whichever order they spontaneously occur) and discovered transference (the process in which patients displace on to their analysts feelings derived from their childhood objects), establishing its central role in the analytic process.
Freud's redefinition of sexuality to include its infantile forms led him to formulate the Oedipus Complex as the central tenet of psychoanalytical theory. His analysis of his own and his patients' dreams as wish-fulfillments provided him with models for the clinical analysis of symptom formation and the mechanisms of repression as well as for elaboration of his theory of the unconscious as an agency disruptive of conscious states of mind.
Freud postulated the existence of libido, an energy with which mental process and structures are invested and which generates erotic attachments, and a death drive, the source of repetition, hate, aggression and neurotic guilt. In his later work Freud drew on psychoanalytic theory to develop a wide-ranging interpretation and critique of religion and culture.