Dr. Mark Harper, MD, PhD, is a consultant anesthetist at Sussex University Hospitals in the UK and Kristiansand in Norway. He is a leading expert in the prevention of hypothermia in surgical patients and the therapeutic uses of cold-water adaptation and open-water swimming. He has been featured in the BBC documentary The Doctor Who Gave Up Drugs, is a cocreator of Chill UK, a nonprofit committed to providing courses in cold-water swimming to improve mental health, and the director of Mental Health Swims. He lives in England and Norway.