After running Snowball off the farm, Napoleon becomes the leader. At the end of the book, Napoleon becomes a corrupted leader and, standing on two legs just like the formerly hated humans, reverts the name of the farm back to Manor Farm.
Napoleon was named after French military leader Napoleon Bonaparte. Because of his rise to power and subsequent ruling styles, the name Napoleon has become synonymous with dictators and the idea the power can corrupt. This is fitting in the case of Animal Farm where this Napoleon raises to power after making secret deals with neighbors and kills numerous friends who confess to chasing Snowball off the farm, when in fact it was he who drove off his former friend.