High Quality Content by WIKIPEDIA articles! 'X' Stands for Unknown is a collection of seventeen nonfiction science essays written by Isaac Asimov. It was the seventeenth of a series of books collecting essays from The Magazine of Fantasy and Science Fiction, these being first published between January 1982 and May 1983. It was first published by Doubleday & Company in 1984. Isaac Asimov (born Isaak Yudovich Ozimov, Russian: ; c. 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.