Founding chairman of the Chinese Communist Party, leader of the Chinese Revolution, and — by sheer demographic and geopolitical consequence — one of the most historically influential figures of the 20th century. Mao's writings adapted Marxism-Leninism to a predominantly peasant society and produced, for good and catastrophic ill, a distinct body of revolutionary political theory that shaped Chinese history from the 1927 split with the Kuomintang through the Long March (1934–35), the war against Japan, the victory over the Nationalists in 1949, the Great Leap Forward (1958–62), and the Cultural Revolution (1966–76).
The theoretical contribution is real and has to be separated, analytically if not morally, from the human toll of its application. Against orthodox Marxist insistence on the urban industrial proletariat as the revolutionary subject, Mao argued — in Report on an Investigation of the Peasant Movement in Hunan (1927) and the later Yan'an essays — that in a society like China's the peasantry was the main revolutionary force and that protracted people's war, surrounding the cities from the countryside, was the adequate strategy. On Contradiction (1937) and On Practice (1937) are his attempts to ground a dialectical theory of political struggle in Chinese idiom; On New Democracy (1940) articulated the transitional political form he thought appropriate to a semi-colonial, semi-feudal society.
The regime Mao built delivered genuine social transformations — mass literacy, extended life expectancy, the abolition of warlord and foreign control, a degree of gender reform — and presided over catastrophes of historically unusual scale. The Great Leap's famine killed somewhere between fifteen and forty-five million people (estimates vary); the Cultural Revolution destroyed a generation of Chinese intellectual and institutional life and killed perhaps a million more directly. His influence beyond China — on Third World anticolonial movements, on European left thought of the 1960s (Sartre, Althusser, and the French Maoists), on Latin American guerrilla theory (the Shining Path in Peru, the Naxalites in India) — was large, uneven, and in most places has outlasted sober assessment of the original project.