In 1964, the British psychologist Hans Jürgen Eysenck published Crime and Personality, the book that set forth his theory of the criminal as a psychopathic poor conditioner. Crime and Personality went through three editions, and even those who vehemently rejected the theory acknowledged it as the most highly articulated and influential biological explanation of crime of its time. Yet today Eysenck’s name is fading from criminological memory - and none too soon, in the opinion of critics who continue to anathematize (...) him as a self-serving showman, charlatan, and dangerous right-wing conservative. This article addresses four questions. Who was Eysenck? What did he say about the causes of crime? Why was he (and why does he continue to be) such a controversial figure? And did he contribute any ideas of lasting significance to criminology? The answers open a window onto the late 20th-century revival of biocriminology, a return to biological explanations that continues into the present and seems to be accelerating. They also reveal characteristics of criminology itself as a knowledge enterprise that has changed over time. (shrink)