Umbra

[T]he tide that rose in the unconscious after the first World War was reflected in individual dreams, in the form of collective mythological symbols which expressed primitivity, violence, cruelty: in short, all the powers of darkness. When such symbols occur in a large number of individuals and are not understood, they begin to draw these individuals together as if by magnetic force, and thus a mob is formed. Its leader will soon be found in the individual who has the least resistance, the least sense of responsibility and, because of his inferiority, the greatest will to power. He will let loose everything that is ready to burst forth, and the mob will follow with the irresistible force of an avalanche. [...] He was the most prodigious personification of all human inferiorities. He was an utterly incapable, unadapted, irresponsible, psychopathic personality, full of empty, infantile fantasies, but cursed with the keen intuition of a rat or a guttersnipe. He represented the shadow, the inferior part of everybody's personality, in an overwhelming degree, and this was another reason they fell for him. 

Carl Gustav Jung, "The Fight with the Shadow", 

first published in The Listener (London), XXXVI (1946), no. 930, 615-16.