The influential psychologist known for their research in human development is Jean Piaget. He is recognized for his pioneering work on cognitive development in children, outlining stages through which children progress as they learn. Piaget's theories emphasize the importance of play and exploration in young minds, illustrating how children construct their understanding of the world. His work has had a profound impact on education, informing teaching methods and child psychology. Piaget’s legacy endures in ongoing studies of cognitive growth and developmental psychology.