Sigmund Freud (born Sigismund Schlomo Freud (May 6, 1856 – September 23, 1939), was a Jewish-Austrian neurologist who founded the psychoanalytic school of psychiatry. 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 (technically referred to as an "analysand") 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. Freud was also a prolific essayist, drawing on psychoanalysis to contribute to the history, interpretation and critique of culture.

While some 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 some of his theories, Freud's work remains seminal in humans' quest for self-understanding, especially in the history of clinical approaches. In academia, his ideas continue to influence the humanities and social sciences. He is considered one of the most prominent thinkers of the first half of the 20th century, in terms of originality and intellectual influence.

Freud was born on May 6, 1856, to Jewish Galician parents in the Moravian town of Příbor, Austrian Empire, which is now part of the Czech Republic. Freud was born with a caul, which the family accepted as a positive omen. His father, Jakob, was 41, a wool merchant, and had two children by a previous marriage. His mother, Amalié (née Nathansohn), the second wife of Jakob, was 21. He was the first of their eight children and, owing to his precocious intellect, his parents favoured him over his siblings, since the early stages of his childhood. Despite their poverty, they sacrificed everything to give him a proper education. Due to the economic crisis of 1857, Freud's father lost his business, and the family moved to Leipzig before settling in Vienna. In 1865, Sigmund entered the Leopoldstädter Kommunal-Realgymnasium, a prominent high school. Freud was an outstanding pupil and graduated the Matura in 1873 with honors.

After planning to study law, Freud joined the medical faculty at University of Vienna to study under Darwinist Prof. Karl Claus. At that time, the eel life cycle was still unknown. In search of their male sex organs, Freud spent four weeks at the Austrian zoological research station in Trieste, dissecting hundreds of eels without finding more than his predecessors had. While Freud was a first-year medical student at the University of Vienna, he was supervised by German physiologist Ernst Wilhelm von Brücke. Freud adopted Brücke's new "dynamic" physiology. In 1874, the concept of "psychodynamics" was proposed by Brücke, with the publication of Lectures on Physiology. Brücke, in coordination with physicist Hermann von Helmholtz, one of the formulators of the first law of thermodynamics (conservation of energy), supposed that all living organisms are energy-systems also governed by this principle. In his Lectures on Physiology, Brücke set forth the radical view that the living organism is a dynamic system to which the laws of chemistry and physics apply.

This was the starting point for Freud's dynamic psychology of the mind and its relation to the unconscious. The origins of Freud’s basic model, based on the fundamentals of chemistry and physics, according to John Bowlby, stems from Brücke, Meynert, Breuer, Helmholtz, and Herbart. In 1876, he published his first paper about "the testicles of eels" in the Mitteilungen der österreichischen Akademie der Wissenschaften, conceding that he could not solve the matter. In 1877, Freud abbreviated his first name from "Sigismund" to "Sigmund."

In 1879, Freud interrupted his studies to complete his one year of obligatory military service, and in 1881 he received his Dr. med. (M.D.) with the thesis Über das Rückenmark niederer Fischarten ("on the spinal cord of lower fish species").

In October 1885, Freud went to Paris on a traveling fellowship to study with Europe's most renowned neurologist, Jean Martin Charcot. He was later to remember the experience of this stay as catalytic in turning him toward the practice of medical psychopathology and away from a less financially promising career in research neurology. Charcot specialised in the study of hysteria and its susceptibility to hypnosis, which he frequently demonstrated with patients on stage in front of an audience. Freud later turned away from hypnosis as a potential cure, favouring free association and dream analysis. Charcot himself questioned his own work on hysteria towards the end of his life.

After opening his own medical practice, specializing in neurology, Freud married Martha Bernays in 1886. Her father Berman was the son of Isaac Bernays, chief rabbi in Hamburg. After experimenting with hypnosis on his neurotic patients, Freud abandoned this form of treatment as it proved ineffective for many, in favor of a treatment where the patient talked through his or her problems. This came to be known as the "talking cure", as the ultimate goal of this talking was to locate and release powerful emotional energy that had initially been rejected, and imprisoned in the unconscious mind. Freud called this denial of emotions "repression", and he believed that it was often damaging to the normal functioning of the psyche, and could also retard physical functioning as well, which he described as "psychosomatic" symptoms. (The term "talking cure" was initially coined by the patient Anna O. who was treated by Freud's colleague Josef Breuer.) The "talking cure" is widely seen as the basis of psychoanalysis. Carl Jung initiated the rumor that a romantic relationship may have developed between Freud and his sister-in-law, Minna Bernays, who had moved into Freud's apartment at 19 Berggasse in 1896. (Psychologist Hans Eysenck has suggested that the affair resulted in a pregnancy and a subsequent abortion for Miss Bernays.) The publication in 2006 of a Swiss hotel log, dated 13 August 1898, has suggested to some Freudian scholars that there was a factual basis to these rumors.

In his 40s, Freud "had numerous psychosomatic disorders as well as exaggerated fears of dying and other phobias". During this time, Freud was involved in the task of exploring his own dreams, memories, and the dynamics of his personality development. During this self-analysis, he came to realize the hostility he felt towards his father (Jacob Freud), who had died in 1896, and "he also recalled his childhood sexual feelings for his mother (Amalia Freud), who was attractive, warm, and protective". This time of emotional difficulty was the most creative time in Freud's life.

After the publication of Freud's books in 1900 and 1902, interest in his theories began to grow, and a circle of supporters developed in the following period. However, Freud often clashed with those supporters who critiqued his theories, the most famous being Carl Jung, who had originally supported Freud's ideas. Part of the reason for the fallout between Freud and Jung was the latter's interest and commitment to religion, which Freud saw as unscientific.

In 1932, Freud received the Goethe Prize in appreciation of his contribution to psychology and to German literary culture. One year later (on January 30th, 1933), the Nazis took control of Germany, and Freud's books were prominent among those burned and destroyed by the Nazis. At that time, he could not have foreseen that all of his many sisters would perish in The Holocaust.
In March 1938, Nazi Germany annexed Austria in the Anschluss. This led to violent outbursts of anti-Semitism in Vienna, and Freud and his family received visits from the Gestapo. Freud decided to go into exile "to die in freedom". In this goal, he was fortuitously assisted by Anton Sauerwald, a Nazi official who was placed in charge of all of Freud's assets in Austria. Sauerwald, however, was not an ordinary Nazi; while "he had made bombs for the Nazi movement, he had also studied medicine, chemistry and law." At the University of Vienna, Sauerwald had been a student of Professor Josef Herzig, who often visited Freud to play cards. Sauerwald did not disclose to his Nazi superiors that Freud had many secret bank accounts and disobeyed a Nazi directive to have Freud's books on psychoanalysis destroyed. Instead, Sauerwald and an accomplice smuggled them to the Austrian national library, where they were hidden. Finally, dismayed by a Nazi order to transform Freud's home into an institute for the study of Aryan superiority, Sauerwald signed Sigmund Freud's exit visa. In June 1938, Freud left Vienna aboard the Orient Express train and settled in London. While Freud told a local newspaper that "all my money and property in Vienna is gone", he did not mention his secret bank accounts. When Anton Sauerwald went to trial on charges of absconding with Freud’s secret wealth after the war, Anna Freud, Sigmund Freud's daughter, intervened to protect Sauerwald. She disclosed to Harry Freud, a US army officer who had had Sauerwald arrested. Sauerwald was then released from U.S. custody. After arriving in Britain, Freud and his family settled in 20 Maresfield Gardens, Hampstead, London. There is a statue of him at the corner of Belsize Lane and Fitzjohn's Avenue, near Swiss Cottage.

A heavy cigar smoker, Freud endured more than 30 operations during his life due to oral cancer. In September 1939, he prevailed on his doctor and friend Max Schur to assist him in suicide. After reading Balzac's La Peau de chagrin in a single sitting, he said, "My dear Schur, you certainly remember our first talk. You promised me then not to forsake me when my time comes. Now it is nothing but torture and makes no sense anymore." Schur administered three doses of morphine over many hours that resulted in Freud's death on 23 September 1939. Three days after his death, Freud's body was cremated at Golders Green Crematorium in England during a service attended by Austrian refugees, including the author Stefan Zweig. His ashes were later placed in the crematorium's columbarium. They rest in an ancient Greek urn that Freud received as a present from Marie Bonaparte, and which he had kept in his study in Vienna for many years. After Martha Freud's death in 1951, her ashes were also placed in that urn. Golders Green Crematorium has since also become the final resting place for Anna Freud and her lifelong friend Dorothy Burlingham.