Daniel John Callahan (July 19, 1930 – July 16, 2019) was an American philosopher who played a leading role in developing the field of biomedical ethics as co-founder of The Hastings Center, the world's first bioethics research institute. He served as the Director of The Hastings Center from 1969 to 1983, president from 1984 to 1996, and president emeritus from 1996 to 2019. He was the author or editor of 47 books.