Charles-Marie Gustave Le Bon[a] (7 May 1841 – 13 December 1931) was a leading French polymath whose areas of interest included anthropology, psychology, sociology, medicine, invention, and physics.

He analysed the peoples and the civilisations he encountered under the umbrella of the nascent field of anthropology, developing an essentialist view of humanity, and invented a portable cephalometer during his travels.

At the same time he created his psychological and sociological theories, he performed experiments in physics and published popular books on the subject, anticipating the mass–energy equivalence and prophesising the Atomic Age.

Ignored or maligned by sections of the French academic and scientific establishment during his life due to his politically conservative and reactionary views, Le Bon was critical of majoritarianism and socialism.

[7] When Le Bon was eight years old, his father obtained a new post in French government and the family, including Gustave's younger brother Georges, left Nogent-le-Rotrou never to return.

During his university years, Le Bon wrote articles on a range of medical topics, the first of which related to the maladies that plagued those who lived in swamp-like conditions.

[10] He maintained his passion for writing and authored several papers on physiological studies, as well as an 1868 textbook about sexual reproduction, before joining the French Army as a medical officer after the outbreak of the Franco-Prussian War in July 1870.

"[14] He also warned his countrymen of the deleterious effects of political rivalries in the face of German military might and rapid industrialisation, and therefore was uninvolved in the Dreyfus Affair which dichotomised France.

Influenced by Charles Darwin, Herbert Spencer and Ernst Haeckel, Le Bon supported biological determinism and a hierarchical view of the races and sexes; after extensive field research, he posited a correlation between cranial capacity and intelligence in Recherches anatomiques et mathématiques sur les variations de volume du cerveau et sur leurs relations avec l'intelligence (1879), which earned him the Godard Prize from the French Academy of Sciences.

[11] The results of his journeys were a number of books, and a development in Le Bon's thinking to also view culture to be influenced chiefly by hereditary factors such as the unique racial features of the people.

"[25] Le Bon released the last book on the topic of his travels, entitled Les monuments de l'Inde, in 1893, again praising the architectural achievements of the Indian people.

This work became a respected cavalry manual, and Le Bon extrapolated his studies on the behaviour of horses to develop theories on early childhood education.

[28] Le Bon's behavioural study of horses also sparked a long-standing interest in psychology, and in 1894 he released Lois psychologiques de l'évolution des peuples.

[29] Psychologie des Foules was in part a summation of Le Bon's 1881 work, L'Homme et les sociétés, to which Émile Durkheim referred in his doctoral dissertation, De la division du travail social.

[32] Le Bon constructed a home laboratory in the early 1890s, and in 1896 reported observing "black light", a new kind of radiation that he believed was distinct from, but possibly related to, X-rays and cathode rays.

[38][39] He wrote about "the manifestation of a new force—namely intra-atomic energy—which surpasses all others by its colossal magnitude," and stated that a scientist who discovered a way to dissociate rapidly one gram of any metal would "not witness the results of his experiments ... the explosion produced would be so formidable that his laboratory and all neighbouring houses, with their inhabitants, would be instantaneously pulverised.

He then released Psychologie des Temps Nouveaux (1920) before resigning from his position as Professor of Psychology and Allied Sciences at the University of Paris and retiring to his home.

He published his last work, entitled Bases scientifiques d'une philosophie de l'histoire, in 1931 and on 13 December, died in Marnes-la-Coquette, Île-de-France at the age of ninety.

[45] Le Bon theorised that the new entity, the "psychological crowd", which emerges from incorporating the assembled population not only forms a new body but also creates a collective "unconsciousness".

For Le Bon, the crowd inverts Darwin's law of evolution and becomes atavistic, proving Ernst Haeckel's embryological theory: "ontogeny recapitulates phylogeny".

Trotter's book Instincts of the Herd in Peace and War (1919) forms the basis for the research of both Wilfred Bion and Ernest Jones who established what would be called group dynamics.