American Baptist minister, leader of the civil rights movement from the 1955–56 Montgomery Bus Boycott until his assassination in 1968, and — through speeches, sermons, and books — one of the most influential American moral theorists of the 20th century. King's doctoral training at Boston University (on Paul Tillich and Henry Nelson Wieman) and his reading of Gandhi, Thoreau, Rauschenbusch's social gospel, and the Black church tradition gave him an unusually rich theoretical foundation for what was, in its essence, a practical political ministry.
His central argument is that non-violent resistance, far from being passivity, is the morally and strategically superior response to systemic injustice. Violence corrupts those who use it and provides oppressors with the pretext they need; disciplined non-violence exposes the violence of the unjust order and places the moral weight of public conscience on the side of the oppressed. The Letter from Birmingham Jail (1963) — written on the margins of a newspaper in response to moderate white clergy who urged him to wait — is the single most sustained statement of this case and the most important American political document of the second half of the century.
King's thought developed significantly between 1955 and 1968. The early King emphasized integration within the American dream; the later King, shaped by the persistence of northern racism and the Vietnam War, pressed toward a more structural critique of capitalism, militarism, and what he called the "giant triplets" of racism, materialism, and militarism. His Poor People's Campaign and his increasing focus on economic justice made him, at his death, more politically radical than the figure later domesticated into statues and national holiday.