Harry Harlow (1906-1981) was an American psychologist best known for his studies on affection and development using rhesus monkeys and surrogate wire or terrycloth mothers. He earned his BA and Ph.D. from Stanford University, and did his research primarily at the University of Wisconsin where he worked for a time with humanistic psychologist Abraham Maslow.

He was well-known for refusing to use euphemism and instead chose deliberately outrageous terms for the experimental apparatus he devised, including a forced mating device he called a "rape rack", tormenting surrogate mother devices he called "iron maidens" and an isolation chamber he called the "pit of despair."

His most famous experiment, in which rhesus monkeys choose between the the terrycloth mothers and food, was discovered fradulent as he omitted important data. Specifically, the one warehouse in which the monkeys choose the "warm, loving, and tender" mother lacked central heating and the monkeys starved rather than freeze to death with the wire providing food. In another, unsubmitted, trial the monkeys would hang on to the food-providing figure. These records were discovered upon his death.

In the latter of these devices, alternatively called the "well of despair", baby monkeys would be hung upside-down in darkness for a period of up to two years. Unsurprisingly, this procedure produced monkeys that were severely psychologically disturbed. Perhaps ironically, Harlow's experiments showed the importance of affection and nurturance on psychological development. He often said he wanted to study love, which he thought was being ignored by then-behaviorist dominated psychology. However, many of his experiments would probably be considered unethical today.

In 1958, he was elected president of the American Psychological Association, at which time he presented his seminal paper, On the Nature of Love.