Urie Bronfenbrenner was a pioneering developmental psychologist known for establishing the ecological systems theory of human development. The ecological systems theory proposes that human development is influenced by different environmental systems, including the microsystem of immediate relationships, the mesosystem of connections between microsystems, the exosystem of external social settings, the macrosystem of cultural values and beliefs, and the chronosystem of time and life transitions. Bronfenbrenner recognized that to understand child development, one must consider the entire ecological system of relationships and environments within which growth occurs. His work laid the foundation for examining how factors like family, school, neighborhood, and culture interact to influence how individuals grow and develop.