B.F. Skinner was an American psychologist known for his work on operant conditioning. He invented the Skinner box to study behavior through positive and negative reinforcement. Using hungry rats in the Skinner box, Skinner found that they would learn to press a lever for food pellets, showing how positive reinforcement strengthens behaviors. Based on his experiments, Skinner developed the theory of operant conditioning, which argues that behaviors are shaped by their consequences in the environment rather than free will.