Final answer:
Theories of intelligence began to emerge in a formal way during the early 20th century, with foundational work by Alfred Binet and later contributions by figures such as Louis Terman and David Wechsler who developed widely used intelligence tests.
Step-by-step explanation:
Theories of intelligence began emerging in earnest during the early 20th century. One of the key figures in the history of intelligence testing was Alfred Binet, who was tasked by the French government to develop an intelligence test for children to identify potential difficulties in school. This ushered in the era of formal intelligence testing, with Binet's tests involving many verbally based tasks. Following Binet's pioneering work, Louis Terman modified these tasks and introduced the concept of standardization in test administration. These early tests formed the basis of what would become the Stanford-Binet Intelligence Scales. Additionally, Sir Francis Galton had developed the first broad test of intelligence in the late 1800s, and although it was not as refined as Binet's, it marks one of the starting points in the measurement and understanding of intelligence.
The development of the IQ test most widely used today, however, is credited to David Wechsler. Wechsler's intelligence tests, including the WAIS-IV and WISC-V, continue to be used extensively. These advancements in the field of intelligence research have evolved from the early philosophical discussions of thinkers like Aristotle, who contemplated the nature of intelligence long before modern psychology's establishment.