Melanie Klein was an Austrian-British psychoanalyst who developed object relations theory. She believed that infants as young as 4 months old engage in psychic life involving phantasies of good and bad breast objects, and employ defense mechanisms like splitting, projection, and introjection to manage anxiety from destructive impulses. Klein argued the superego and Oedipus complex emerge much earlier than Freud theorized, with the superego instilling terror rather than guilt in young children. Her theories challenged and extended Freud's work through observations of children too young for traditional psychoanalysis.