French Marxist philosopher who, from his post at the École normale supérieure, did more than anyone else in the 1960s to turn Marxism into a rigorous structural science and to train a generation of French radicals — Rancière, Balibar, Macherey, Badiou, Derrida's early readers — in that discipline. Born in French Algeria and a prisoner of war from 1940 to 1945, he joined the French Communist Party in 1948 and remained inside it, as a loyal but increasingly heterodox member, for the rest of his working life. His two manifesto-books — For Marx (1965) and Reading Capital (1965, with his ENS students) — proposed that Marx's mature work constituted a new science of history, separated from his Hegelian-humanist juvenilia by a Bachelardian "epistemological break." Theory, properly done, was not the expression of class consciousness but a specific kind of labor on concepts; the working class needed philosophers the way it needed engineers.
His most durable contributions are in the theory of Ideology. In the 1970 essay "Ideology and Ideological State Apparatuses" he argued that capitalist societies reproduce themselves not mainly through the Repressive State Apparatus (police, army, courts) but through a plural network of Ideological State Apparatuses — school, church, family, media, trade union, political party — which shape subjects into functioning bearers of their social roles. Ideology for Althusser is not false belief but a lived relation: it interpellates individuals, hailing them into subject-positions the way a cop calls "Hey, you!" and the person who turns is thereby constituted as guilty, addressed, a subject. The essay became foundational for cultural studies (Stuart Hall took it to Birmingham), film theory, and post-colonial analysis.
His career was lived under the shadow of severe manic-depressive illness and repeated psychiatric hospitalizations. In November 1980, during a psychotic episode, he strangled his wife Hélène Rytmann, a sociologist and his intellectual companion of decades; a French court found him unfit to stand trial and committed him to the Sainte-Anne hospital. He never returned to teaching, and the posthumously published The Future Lasts Forever (1992) is at once memoir, apology, and self-analysis — unsparing and inadequate at the same time. The philosophical project was already fracturing before the killing, as former students (Jacques Rancière first among them) attacked the scientist-masses hierarchy built into his account of theory; the event closed it. Contemporary returns to Althusser — in Badiou, in cultural theory, in revivals of "aleatory materialism" from his late notebooks — tend to read him against himself, past the structural scaffolding and toward the late, messier Althusser of Philosophy of the Encounter.