Isaac Asimov (born Isaak Yudovich Ozimov, January 2, 1920 – April 6, 1992) was an American author and professor of biochemistry at Boston University, best known for his works of science fiction and for his popular science books. Asimov was one of the most prolific writers of all time, having written or edited more than 500 books and an estimated 9,000 letters and postcards. His works have been published in nine of the ten major categories of the Dewey Decimal System (The sole exception being the 100s: philosophy and psychology, although he did write a foreword for The Humanist Way, which is published in the 100s).