How does Napoleon change as he exerts more control in Animal Farm?
As the animal revolution begins, Napoleon works mostly behind the scenes, sharing leadership with Snowball and not directly affecting the farm's operation. His only major contribution is to distract the animals from the final use of the cow's milk. However, as the following quote shows, he is more concerned with creating a power-base for himself than with the farm's success:
It happened that Jessie and Bluebell had both whelped soon after the hay harvest, giving birth between them to nine sturdy puppies. As soon as they were weaned, Napoleon... kept them in such seclusion that the rest of the farm soon forgot their existence.
(Orwell, Animal Farm, msxnet.org)
By acquiring a personal army, Napoleon is able to expel Snowball and take the leadership role for himself. The other pigs quickly see the merit in going along with Napoleon, since he is able to provide them better food than the other animals. He moves from being a single facet of the revolution -- in which all the animals are supposedly equal -- to a dictator, executing animals for dissension and changing the Laws of Animalism to suit his own desires.