John B. Carroll was an American psychologist known for his work in the field of intelligence and educational psychology. He is best recognized for developing the Carroll's Three-Stratum Theory of Intelligence, which categorizes cognitive abilities into three levels: general intelligence, broad abilities, and narrow abilities. This framework has influenced both research and practical applications in understanding human intelligence. Carroll's contributions extended to the development of the Woodcock-Johnson Tests of Cognitive Abilities, a widely used assessment tool in educational settings. His research emphasized the importance of distinguishing between different types of cognitive skills, helping educators tailor their approaches to meet diverse learning needs.