Leon Richard Kass (born February 12, 1939) is an American physician, scientist, educator, and public intellectual, best known as proponent of liberal education via the "Great Books," as an opponent of human cloning, life extension and euthanasia, as a critic of certain areas of technological progress and embryo research, and for his controversial tenure as chairman of the President's Council on Bioethics from 2001 to 2005.