It's not a biopic.
Ok, of course this is something you already knew about The Shawshank Redemption but as the movie was gearing up for production, this was actually very unclear. Frank Darabont had to shorten the movie's name from King's original title, Rita Hayworth and the Shawshank Redemption, after agents kept pitching actresses for the lead.
Stephen King licensed the story for a dollar.
Since 1976, the prolific author has offered the Dollar Baby deal. The Master of Horror will let aspiring filmmakers adapt his short stories for a single U.S. dollar. Contrary to how some have interpreted this, King still retains the rights to the stories. It's more of a license for noncommercial use.