Hugh Herr (born October 25, 1964) is an American rock climber, engineer, and biophysicist. When he was young, both of his legs were amputated below the knee due to an accident during an unexpected blizzard that occurred on a rock climbing trip. After months of surgeries and rehabilitation, Herr began climbing again, using specialized prostheses he designed for himself. He holds the patents to the Rheo Knee, an active ankle-foot orthosis, which is the world's first powered ankle-foot prosthesis.