Hans Eysenck was a prominent psychologist known for his work in personality theory and psychometrics. He developed the Pen model of personality, which categorized individuals into extroversion, introversion, and later two additional dimensions: neuroticism and psychoticism. Eysenck believed that these traits were influenced by genetics and biology and argued that personality is largely stable throughout an individual's life. In addition to his theories on personality, Eysenck was also known for his controversial views on intelligence and the influence of heredity on mental abilities. He often engaged in debates about the racial aspects of intelligence, positing that differences in IQ scores among different ethnic groups might be rooted in genetic factors, a stance that drew significant criticism over the years. Eysenck's contributions to psychology were extensive, including numerous publications and the development of various psychological assessments. His influence persists in both personality psychology and psychometric evaluations, although many of his ideas remain contentious and continue to inspire discussion and research. Hans Eysenck was a leading figure in psychology, renowned for his research in personality and intelligence. His Pen model of personality classified traits into extroversion, introversion, neuroticism, and psychoticism, emphasizing genetic and biological influences. Despite his significant contributions, Eysenck's views, particularly on intelligence and race, have sparked considerable debate and controversy in the field.