Captain Book is a term used to refer to two famous fictional captains from literature. The first is Captain Nemo, the protagonist of Jules Verne's novel '20, 000 Leagues Under the Sea'. He was a mysterious and enigmatic figure who commanded the submarine Nautilus. The second is Captain Ahab, the antagonist of Herman Melville's novel 'Moby Dick'. He was an obsessive and vengeful captain who was determined to hunt down the white whale Moby Dick.