The first IQ test was conducted way back in 1904. French government officials requested Alfred Binet , a french psychologist, to help them find out the students that struggled in school so that they could be helped.
Alfred, along with his colleague Theodore Simon prepared a test with different questions. These questions were from different walks of life, but most were related to practical matters like problem-solving, attention, and memory.
Since these topics were not typically taught to students in schools, both Alfred and Simon agreed that this was the best way to filter out students.
The test turned out to be a success as some kids were able to answer questions beyond their age. Here's where the concept of mental age came into being.
This was the first IQ test conducted by Alfred and Simon. However, the test went through several changes as different experts gave their own inputs on the concept.