What two leaders emerge after the rebellion in "Animal Farm?"

In George Orwell's "Animal Farm," the main leaders of the animals after the rebellion are two pigs, Napoleon and Snowball.

These two pigs aren't the ones who came up with the idea of rebelling.  It was another pig, Old Major, who did that.  But Old Major dies soon after starting the rebellion and Napoleon and Snowball come to lead it.

As the story wears on, Napoleon and Snowball become enemies as they fight for control of their revolution.  Eventually, Napoleon wins and Snowball is driven off the farm.

Napoleon and Snowball are meant to represent Josef Stalin and Leon Trotsky, respectively.