B.F. Skinner was an American psychologist who developed the theory of operant conditioning. He believed that learning is based on consequences and that behaviors are strengthened or weakened based on reinforcement and punishment. Skinner's theory of operant conditioning built upon Thorndike's law of effect and introduced the concept of reinforcement. Operant conditioning focuses on how voluntary behaviors are influenced by environmental consequences and can be used to shape behaviors through positive or negative reinforcement or punishment. Skinner's theory has influenced instructional methods like direct instruction and the use of technology in education.