According to the Mayo Clinic, the Atkins diet was invented in 1972 by cardiologist Robert C. Atkins. The diet's defining feature is its emphasis on the role of carbohydrates in weight gain. The earliest version of the Atkins diet focused exclusively on nutrition and excluded exercise requirements.
Dr. Atkins was motivated to develop the diet to address his own weight issues in the early 1960s. According to Wikipedia, he based his approach on nutrition research done in the 1950s by Dr. Alfred Pennington. Atkins claimed to have lost weight with the plan and began recommending the reduction or outright elimination of sugar and other carbohydrates from dieters' food intake.