Jean Piaget was a Swiss psychologist known for his work in child development. He proposed that children learn through a series of stages, each characterized by different ways of thinking and understanding the world. His theory emphasizes that children actively construct their knowledge through experiences and interactions. Piaget identified four main stages of cognitive development: sensorimotor, preoperational, concrete operational, and formal operational. Each stage represents a different level of cognitive maturity, influencing how children perceive and interact with their environment. His research has significantly impacted education and psychology, shaping how we understand learning processes in children.