Charles-Marie-Gustave Le Bon (May 7, 1841 – December 13, 1931) was a French social psychologist, sociologist, and physicist. He was the author of several works in which he expounded theories of national traits, racial superiority, herd behavior, and crowd psychology. His views on cultural evolution were based on his belief that it is the character or “soul” of the people that determines their progress, and that this character took the form of an unconscious “collective mind.” This collective mind would also emerge in a crowd of people, influencing their behavior in ways not predicted by simply studying an individual.
Le Bon’s thesis that the behavior of crowds was based on emotion rather than intellect was influential in several arenas, with mixed results. His work on crowd psychology was used by media researchers to develop propaganda and advertising techniques to influence the public. These ideas were also adopted by Adolf Hitler as he mobilized large crowds of people to act based on their emotions and fears, often in ways that they would not have done based on their individual beliefs.
Le Bon recognized that his work revealed great dangers to society and he warned that if the masses were to gain control, human society would revert to barbarism. Although his work suggested it, he did not pursue to the more common historical outcome in which a strong leader manipulates the masses to behave in violent, inhumane ways. In this sense, Le Bon’s work was an incomplete analysis of crowd dynamics, while at the same time it did open new avenues of understanding human behavior.
Le Bon’s book – The Crowd  has been referred by some, as one of the major influence on L. Ron Hubbard writings, before he created Dianetics and Scientology. I have formatted the text from the book, with relevant links and images from the website Gutenberg.org and below is a Youtube Audio-book of the text.