Jean Piaget was a Swiss psychologist known as the father of developmental psychology. He spent over 60 years researching cognitive development in children and developed the theory of four stages of cognitive development: sensorimotor, preoperational, concrete operational, and formal operational. According to Piaget, humans construct their own knowledge through experiences that allow for assimilation and accommodation of new information into existing mental models or schemas. He believed education should focus on creating independent thinkers capable of new ideas rather than repetition.