B.F Skinner

He discovered and advanced the rate of response as a dependent variable in psychological research. He invented the cumulative recorder to measure rate of responding as part of his highly influential work on schedules of reinforcement. In a recent survey, Skinner was listed as the most influential psychologist of the 20th century. He was a prolific author who published 21 books and 180 articles.

Theory:
Radical behaviorism seeks to understand behavior as a function of environmental histories of reinforcing consequences.


http://en.wikipedia.org/wiki/B.F_Skinner