Snowball was Napoleon's chief rival in the book Animal Farm. During the Battle of the Cowshed, Snowball leads the way while Napoleon is hiding. Snowball also wants to use a windmill to make the animals' lives easier. Snowball actually believes the tenets of Animalism, while Napoleon wants to use the revolution for his own personal gain. At the height of his power, Snowball is chased from the farm by Napoleon's dogs. Snowball is accused of being a traitor and being an ally of the farmers. Whenever things are going poorly on the farm, Napoleon always blames Snowball in an attempt to shift blame away from himself. Napoleon uses the prospect of Snowball coming back with an army of humans to scare the animals from what should be their main concern—Napoleon and his inner circle reaping the benefits of the revolution while the rest of the animals live horrible lives. In time, Napoleon re-imagines history and places himself at the heart of the revolution and portrays Snowball as a coward and a human sympathizer. In this respect, Snowball is more valuable to Napoleon outside the farm, because he can always use the false memory of Snowball to scare the animals into submission.
The real reason that Snowball is expelled from the farm is that Napoleon regarded him (perhaps correctly) as a dangerous rival. Snowball is intelligent, a gifted leader, and very popular among the other animals. He is the animal most responsible for working the teachings of Old Major into Animalism, and he has been a leader of the revolution since its beginnings. Snowball's relationship with Napoleon begins to sour after the Battle of the Cowshed, with Snowball, (based on Leon Trotsky) disagreeing with Napoleon (Stalin) on two important issues. One is whether the animals should attempt to spread revolution throughout the countryside, and the other is over the construction of a windmill. They have several debates, but Napoleon increasingly uses the sheep to drown out Snowball's speeches. With a public vote on the windmill looming, Napoleon uses his dogs to run Snowball from the farm. He becomes an imagined enemy for the animals, with Squealer always claiming that he is orchestrating a counter-revolution from the outside.