Context: 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.\n\nQuestion: who developed the great man theory of leadership?
Let's think step by step.
Scottish writer Thomas Carlyle
The relevant sentence in the passage is: 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.

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Final answer: Scottish writer Thomas Carlyle