Hans Eysenck was a British psychologist known for his work in personality theory and psychometrics. He developed the Eysenck Personality Questionnaire, which categorizes personality traits into three dimensions: extraversion, neuroticism, and psychoticism. His research emphasized the biological basis of personality and the role of genetics in behavior. Eysenck also contributed to the field of psychotherapy, advocating for the use of empirical research to evaluate therapeutic methods. He published numerous books and articles, influencing both psychology and popular understanding of personality. His ideas sparked debates and discussions, making him a prominent figure in psychology during the 20th century.