# Carl Hovland American psychologist at Yale who pioneered the scientific study of persuasion and attitude change, beginning with research for the U.S. Army's "Why We Fight" films during World War II. Hovland's work established that message effectiveness depends on source credibility, message structure, and audience characteristics — findings that became foundational for [[Propaganda]] research and modern political communication. His "sleeper effect" discovery — that people forget the source of a message while retaining the content — is particularly relevant to understanding how [[Disinformation]] persists even after debunking. *Stub — expand with: Yale Attitude Change Program, Communication and Persuasion (1953), influence on Petty/Cacioppo's Elaboration Likelihood Model, application to modern media manipulation.*