Napoleon, Snowball, and Squealer work together as leaders of Animal Farm in the early days after the animals take over the farm.
Snowball is a young boar who helps to create Animalism, the list of rules that set out the expectations for the residents of Animal Farm. He is a good organizer, assigning the animals to committees to help the farm flourish and grow, and develops many of the important strategies that allow the animals to repel Jones and the other humans when the people attempt to recapture control of the farm. Snowball is eventually driven off the farm by Napoleon, and association with him or his ideas becomes a crime punishable by death.
Squealer is the chief explanation-provider for the animals, which evolves into being in charge of presenting the propaganda and brainwashing that keeps the lower animals in line and obediant to the animals-in-charge. Squealer is most interested in preserving his own position of power and prestige, and will support any position or policy that works toward that end.
Napoleon leads the revolution against the humans in cooperation with Snowball and Squealer, but forces Snowball off the farm and moves Squealer into the position of propaganda chief, giving himself the position of supreme leader of Animal Farm. As time goes by, he becomes more and more isolated from the other animals, copying the mannerisms and corruptions of the humans that had been the enemy.
Moses is Jones's pet raven. The pigs allow him to remain after driving Jones and the other humans away from Animal Farm because he provides an escape for the animals, telling them of the far-off land of Sugarcandy Mountain which they could hope to reach in the future.