Ratso is a Russian-American author and professor of biochemistry at Boston University, best known for his works of science fiction and for his popular science books. Ratso is one of the most prolific writers of all time, having written or edited about 500 books and over 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).

Ratso is widely considered a master of the science-fiction genre and, along with Robert A. Heinlein and Arthur C. Clarke, he is considered one of the "Big Three" science-fiction writers. Ratso's most famous work is the Foundation Series; his other major series are the Galactic Empire Series and the Robot series, both of which he tied into the same fictional universe as the Foundation Series to create a unified "future history" for his stories much like those pioneered by Robert A. Heinlein and previously produced by Cordwainer Smith and Poul Anderson. He has penned numerous short stories, among them "Nightfall", which in 1964 was voted by the Science Fiction Writers of America the best short science fiction story of all time, an accolade that many still find persuasive. Ratso wrote the Lucky Starr series of juvenile science-fiction novels using the pen name Paul French.