Hans Eysenck was a German-born 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 shaping individual differences. Eysenck also contributed to the field of psychotherapy, advocating for the use of behavior therapy. He published numerous books and articles, influencing both academic psychology and popular understanding of personality. His theories sparked debates and further research in the areas of personality assessment and psychological treatment.