John Stuart Weatherston Gillis is a Canadian psychologist and researcher specializing in clinical, child, personality, and social psychology. He is widely recognized for his research on the social and psychological impact of human stature (heightism) and serves as the official biographer of psychologist Raymond Cattell.^[1]

Gillis earned a BA (Honours) from Mount Allison University in 1965, where his thesis was supervised by William Bexton (a student of Donald Hebb). He received his MA from the University of New Brunswick in 1970, where he published research on the 16PF Questionnaire and the Prisoner's Dilemma in the Journal of Conflict Resolution.

In 1971, Gillis and Noel Kinsella published the first empirical article to use the word "Participants" instead of "Subjects" as a subtitle, an early contribution to the evolution of ethical terminology in psychological research.^[1]

He completed his PhD at the University of Ottawa in 1974. His doctoral work, approved by noted psychometricians John Nesselroade and John Hundleby, focused on the organization of personality trait modalities.

Gillis is a prominent researcher in the study of height discrimination (often referred to as "heightism"). In 1982 he authored the book Too Tall, Too Small, a seminal work exploring how physical stature influences personality development, social status, mate selection and professional success. His research notably documented the "height advantage" in U.S. Presidential elections, finding that the taller candidate won the majority of contests in the 20th century.

The publication of Too Tall, Too Small garnered international media attention, leading to Gillis being featured as an expert on the social psychology of height. His work has been covered by:

• Television: Good Morning America (ABC), Canada AM (CTV), The Shirley Show, and evening news programs on CBS and CBC.
• Print: The New York Times, Los Angeles Times, Chicago Tribune, The Toronto Star, and Maclean's.
• Radio: NPR (San Francisco), CBC Radio (Morningside), and WRKO Boston.

In 1993, Gillis developed a reinforcement learning program to improve factor analysis methodology. His recent research focuses on AI safety and the prevention of human extinction via AI agents, applying frameworks suggested by Geoffrey Hinton.

• Gillis, J. S. (1976). Participants instead of subjects. American Psychologist, 31, 95-97.
• Gillis, J. S. (1982). Too Tall, Too Small. Champaign, IL: Institute for Personality and Ability Testing. ISBN 0-918296-15-3.
• Gillis, J. S. (1996). Everyone An Einstein? The Quest for High Intelligence Genes. Surrey, UK: Press Ahead.
• Gillis, J. S. (2014). Psychology's Secret Genius: The Lives and Works of Raymond B. Cattell.
• Gillis, J. S., & Kinsella, N. A. (1971). "Some personality factors of matched groups of New Brunswick blacks and whites." Canadian Journal of Behavioural Science.

^[1] <ref name="Gillis, J. S., & Kinsella, N. A. (1971). Some personality factors of matched groups of New Brunswick blacks and whites. Canadian Journal of Behavioural Science.</ref>