French psychoanalyst, the most influential continental reader of Freud and the single figure through whom psychoanalysis entered the vocabulary of 20th-century French philosophy, literary theory, feminist theory, and film theory. His seminar, delivered continuously in Paris from 1953 to 1980, was attended by most of the figures who would come to define French structuralism and post-structuralism — Althusser, Foucault, Kristeva, Irigaray, Derrida among them — and his written Écrits (1966), though famously difficult, became one of the most cited French books of the century.
Lacan's project announced itself as a return to Freud against what he regarded as the domesticating ego psychology of the post-war American school (the heirs of Anna Freud and Heinz Hartmann). Where that school had placed the adaptive ego at the center, Lacan insisted on the priority of the unconscious — and re-described it in linguistic terms: "the unconscious is structured like a language." Drawing on Saussurean linguistics, Lévi-Strauss's structural anthropology, and Hegelian dialectics, he produced a theoretical vocabulary very different from Freud's biological one: the three registers of the Imaginary, Symbolic, and Real; the mirror stage as the constitutive misrecognition by which the infant assumes a fictitious unified self; the big Other as the field of symbolic norms through which the subject's desire is routed; the objet petit a as the unattainable remainder that drives desire; the Name-of-the-Father as the operator by which a subject enters the symbolic order at all.
His institutional career was turbulent: expelled from the International Psychoanalytical Association in 1963 over his short and variable session lengths, he founded his own École Freudienne de Paris, dissolved it unilaterally in 1980, and left a following that has since split many times. The intellectual influence has been more stable. His concepts shape: Althusser's theory of ideological interpellation; Slavoj Žižek's political philosophy; Judith Butler's account of gender performativity; feminist film theory from Laura Mulvey forward; and the broader project of reading cultural texts through the structure of unconscious desire.
Lacan is forbiddingly difficult to read — deliberately so, on the argument that the resistance of the text mimics the resistance of the symptom. Secondary expositors (Fink, Evans, Žižek in his more didactic mode) are generally where readers new to him begin.
Lacan's place in the graph is principally as hinge: his rereading of Freud became the basis for much of postwar French critical theory, feminist theory (Irigaray, Kristeva), and film studies. His own writing is famously difficult; his role here is as the point at which psychoanalysis meets poststructuralist thought.