B.F. Skinner (1904-1990) was one of the most influential and controversial figures in 20th century psychology. Skinner is the founder of the Behaviorist school of psychology, holding that free will is an illusion and all human behavior is the result of actions on the part of the individual. Skinner discounted the role of the psyche in human motivation, and his work has been highly influential on American education.
Skinner received a Ph.D. from Harvard in 1931, and eventually returned there, in 1958, to serve as a professor until his retirement. Over the course of his career, Skinner developed what he called "Radical behaviorism." Under this theory of psychology, human behavior results from consequences from actions. This is the polar opposite of cognitive psychology, which puts motivations for behavior deep inside the individual's psyche.
Skinner maintained that behavior could be reinforced, either positively or negatively, and thus encouraged or distinguished. Through his experimentation, Skinner developed a schedule of reinforcement that tended to strengthen desired results.
Additionally, Skinner invented several key tools for modern psychology, including the operant conditioning chamber, but also the air crib, the cumulative recorder, and the teaching machine, which administered a program of instruction and rewarded the student for correct answers.