Hans Jürgen Eysenck^[1] (/ˈaɪzɛŋk/; 4 March 1916 – 4 September 1997) was a German-born British psychologist who spent his professional career in Great Britain. He is best remembered for his work on intelligence and personality, although he worked on other issues in psychology.^[2][3] At the time of his death, Eysenck was the living psychologist most frequently cited in the peer-reviewed scientific journal literature.^[4][5] A 2019 study found him to be the third most controversial of 55 intelligence researchers.^[6]

Eysenck's research purported to show that certain personality types had an elevated risk of cancer and heart disease. Some scholars claim to have identified errors and suspected data manipulation in Eysenck's work, and large replications have failed to confirm the relationships that he purported to find. An enquiry on behalf of King's College London found the papers by Eysenck to be "incompatible with modern clinical science".^[7]