The great man theory is a 19th-century idea according to which history can be largely explained by the impact of great men, or heroes; highly influential individuals who, due to either their personal charisma, intelligence, wisdom, or political skill used their power in a way that had a decisive historical impact. The theory was popularized in the 1840s by Scottish writer Thomas Carlyle. But in 1860 Herbert Spencer formulated a counter-argument that has remained influential throughout the 20th century to the present: Spencer said that such great men are the products of their societies, and that their actions would be impossible without the social conditions built before their lifetimes.
Carlyle stated that "The history of the world is but the biography of great men", reflecting his belief that heroes shape history through both their personal attributes and divine inspiration. In his book On Heroes, Hero-Worship and the Heroic in History, Carlyle set out how he saw history as having turned on the decisions of "heroes", giving detailed analysis of the influence of several such men (including Muhammad, Shakespeare, Luther, Rousseau, Pericles, Napoleon, and Wagner). Carlyle also felt that the study of great men was "profitable" to one's own heroic side; that by examining the lives led by such heroes, one could not help but uncover something about one's true nature.
Along with Carlyle, American scholar Frederick Adams Woods also supported the great man theory. In his work The Influence of Monarchs: Steps in a New Science of History Woods investigated 386 rulers in Western Europe from the 12th century till the French revolution in the late 18th century and their influence on the course of historical events.