Gustave Le Bon was born on May 7, 1841, in Nogent-le-Retrou. Le Bon practiced medicine in Paris after finishing his medical studies in 1866. In addition he traveled extensively in Europe, Asia, and North Africa and composed a series of travelogues and works on archeology and anthropology, including "La Civilisation des Arabes" and "Les Civilisations de l'Inde" (both 1884). Le Bon's fame comes primarily from his book "Psychologie des foules" (1895), with which he became the founder of mass psychology. He proposed the theory that the individual in a crowd, even in a highly developed culture, loses his critical capacities and behaves in a affective, primitive, barbaric way. In the situation of the crowd, the individual is easily convinced and is subject to the psychological contagion which allows leaders to easily steer crowds where they please. Le Bon took an active part in the intellectual life of his time and maintained contact to personages such as the philosophers Paul Valéry and Henri Bergson. He published numerous works on other subjects, such as hygiene, psysiology, politics, and sociology. Le Bon died on December 15, 1931, in Paris.