Dean Ornish is an American physician and researcher known for his work in lifestyle medicine. He is the founder of the Ornish Diet, which emphasizes a plant-based, low-fat diet, regular exercise, and stress management techniques. His research has shown that these lifestyle changes can reverse heart disease and improve overall health. Ornish has authored several books and has been involved in various health initiatives. He is also the founder of the Preventive Medicine Research Institute, where he conducts studies on the effects of lifestyle changes on chronic diseases. His work has influenced both medical practice and public health policy.