Hans Jurgen Eysenck (March 4, 1916 - September 4, 1997) was a British psychologist. He was born in Germany, but moved to England in the 1930s because of his opposition to the Nazis. He had interests in a wide range of areas, but he is most remembered for his work in intelligence and personality. He wrote over 50 books and over 900 academic articles in his life and was founder editor of the journal Personality and Individual Differences.

He was professor of psychology at the Institute of Psychiatry (IoP) from 1955 to 1983. Eysenck was a major contributor to the modern scientific theory of personality, a brilliant teacher who also played a crucial role in the establishment of behavioural treatments for mental disorders.

However, the adjective most commonly applied to Eysenck has been "controversial". This is because he has not hesitated to publish material that many people have found ideologically, financially or politically inconvenient, or otherwise objectionable. He is also considered controversial for accepting money from the Pioneer Fund, a eugenics organization.

Publications in which Eysenck's views have roused controversy include (chronologically)

1. A paper in the 1950's purporting to show that psychoanalysis and psychotherapy had no measurable effect.
2. A chapter in Uses and Abuses of Psychology (1953) entitled "What is wrong with psychoanalysis".
3. Race, Intelligence and Education (1971)(The IQ Argument in the U.S.)
4. Sex, Violence and the Media (1978).
5. Astrology - Science or Superstition? (1982)
6. Smoking, Personality and Stress (1991)
7. By far the most acrimonious of the debates has been that over the role of genetics in observed IQ differences, which led to Eysenck famously being punched on the nose during a talk at the London School of Economics.

Eysenck's attitude is summarised in his autobiography Rebel with a Cause (Transaction Publishers (1997), ISBN 1-56000-938-1):

"I always felt that a scientist owes the world only one thing, and that is the truth as he sees it. If the truth contradicts deeply held beliefs, that is too bad. Tact and diplomacy are fine in international relations, in politics, perhaps even in business; in science only one thing matters, and that is the facts."
Eysenck's theory of personality is closely linked with the scales that he and his co-workers developed. These include the Maudsley Medical Questionnaire, Eysenck Personality Inventory (EPI), Eysenck Personality Questionnaire (EPQ) and Sensation Seeking Scale (developed in conjunction with Marvin Zuckerman).