Gary Klein (born February 5, 1944 in New York City, New York, U.S.) is a research psychologist famous for pioneering in the field of naturalistic decision making. By studying experts such as firefighters in their natural environment, he discovered that laboratory models of decision making could not describe it under uncertainty. His recognition primed decision (RPD) model has influenced changes in the ways the Marines and Army train their officers to make decisions. Since 2009, Klein has been a Senior Scientist at MacroCognition LLC.