Eysenck's personality theory, developed by psychologist Hans Eysenck, proposes that personality can be understood through three main dimensions: extraversion, neuroticism, and psychoticism. Extraversion refers to how outgoing and social a person is, while neuroticism relates to emotional stability and the tendency to experience negative emotions. Psychoticism involves traits associated with aggression and interpersonal hostility. Eysenck believed that these dimensions are influenced by biological factors and can be measured through questionnaires. His theory emphasizes that personality traits exist on a continuum, meaning individuals can fall anywhere along these dimensions, rather than fitting into distinct categories.