Louis Althusser was a 20th-century French Marxist philosopher known for his structuralist Marxism and impact on thinkers like Derrida and Foucault. His theories, including concepts of ideology and interpellation, explore how the ruling class maintains dominance through societal beliefs, which are perceived as natural truths. Althusser critiques humanism, asserting that societal structures, rather than individual actions, dictate behavior and creativity.