Douglas Glass · CC BY 4.0

Melanie Klein pioneered child psychoanalysis, developing techniques — using play rather than the couch and free association Freud relied on for adults — that let her interpret the inner lives of children too young to articulate them in words. From that clinical work she built object relations theory, arguing that infants split the world into all-good and all-bad mental images long before they can understand nuance, and that how a child resolves that split shapes adult emotional life — a framework that became one of psychoanalysis's most influential and contested schools of thought.