The first IQ tests were developed in the late 19th century by Paul Broca (1824–1880) and Sir Francis Galton who were interested in finding a way to standardise the method of measuring intelligence.
Interestingly they thought that they could do this by measuring the human skull, the larger — the more intelligent. Luckily, we moved on from this assumption in the early 20th century when Alfred Binet and Theodore Simon put their minds together to create a better way of measuring intelligence.
Employed by the French ministry of education, the scientists were tasked with finding a way to understand who of the children they were testing may be left behind because of lower intelligence compared to children who may just be lazy. The Simon-Binet exam used logical reasoning, finding rhyming words and naming objects as part of their IQ test.
Lewis Terman, an American psychologist revisited the the Simon-Binet exam creating a much more appropriate norm than the original tests so that the quotient could be measured with greater accuracy. The method to measure however only worked with children where the analysis was still based on multiplication of standard figures to find a result.
It was some 30 years later that “David Wechsler solved the problem of calculating adult IQ by simply comparing performance to the distribution of test scores, which is a normal distribution.” His method of analysis and discovering a better way to score these tests have helped create the more modern iterations of the IQ test used across the world.