How did the characters change and evolve throughout the book animal farm?

Napoleon the pig probably had the most drastic change in character, going from a high-minded, populist revolutionary at the beginning to a brutal, self-interested dictator toward the end.

Critics note Orwell's prescience in this matter, since this change in Napoleon's character mirrors the transformation of the leadership of the Soviet Union. The early Bolsheviks were very egalitarian, and valued individual rights; in later years, however, the revolutionary rhetoric became a façade, covering large-scale poverty and exploitation. Animal Farm was published in 1945, well before this latter part of Soviet history took place.