Gustave Le Bon (1841-1931) was a French physician, ethnologist, sociologist and psychologist. He is considered the founder of 'mass psychology'. His famous work 'Psychology of the Masses' exerted a lasting influence in science and practical politics. This fundamental work of social psychology not only influenced Sigmund Freud ('Mass Psychology and Ego Analysis'), but was also used by 20th century politicians and dictators to elaborate their propaganda techniques.