Short answers, pulled from the story.
Louis Althusser was a French Marxist philosopher who taught at the École Normale Supérieure in Paris for 35 years. He is best known for For Marx and Reading Capital, both published in 1965, and for his essay "Ideology and Ideological State Apparatuses" (1970), which introduced the concepts of ISAs and interpellation into social theory.
Althusser argued that Marx's thought underwent a radical epistemological break around 1845, marked by The German Ideology. Before the break, Marx worked within the categories of German Idealism and classical political economy; after it, he developed a fundamentally different theoretical framework built on historical materialism, which Althusser compared in significance to what Thales contributed to mathematics or Galileo to physics.
Althusser defined ideological state apparatuses as the institutions, such as the family, the media, religious organizations, and the education system, through which capitalist societies reproduce the conditions of their own existence. Unlike repressive state apparatuses, which operate through force, ISAs operate primarily through meaning and ideology.
On the 16th of November 1980, Althusser strangled Rytmann in their apartment at the ENS. A psychiatric report concluded he acted during an acute crisis of melancholy in the course of an iatrogenic hallucinatory episode, without realizing what he was doing. The court ruled in February 1981 that he was mentally irresponsible at the time and could not be prosecuted.
Althusser joined the French Communist Party in October 1948 and remained a member for decades while frequently criticizing its positions. He opposed the party's official Stalinist Marxism from the 1960s onward, clashed with party philosopher Roger Garaudy in 1966, and publicly attacked the PCF's decision to abandon the phrase "dictatorship of the proletariat" at its twenty-second congress in 1976.
Althusser developed aleatory materialism, also called the philosophy of the encounter, in short papers drafted from 1982 to 1986 and published posthumously. He argued that there is an underground philosophical current running through thinkers from Democritus to Derrida that emphasizes contingency over general laws of history, and that the conjuncture, the specific historical situation, is the pivotal point at which political practice can intervene.