As you know, Animal Farm is sort of a retelling of the story of the Russian Revolution (not exactly, but generally). The story of Napoleon and Snowball follows the actual events in Russia pretty well. It parallels the struggle for power between Joseph Stalin and Leon Trotsky.
In the early days of the Russian Revolution, Stalin and Trotsky were friends and comrades. But as time went on, Stalin wanted power for himself and saw Trotsky as a threat. So he had Trotsky driven out of Russia into exile. He eventually had Trotsky assassinated, but that is not shown in the book.
One aspect of their characters that is well documented in Animal Farm is Trotsky's (Snowball) intellect vs. Stalin's (Napoleon) vicious treatment of people.
If you took a look at Snowball, he crafted the original master plan of the windmill for the benefit of the animals. He had the idea of seeing the animals improve their comforts and living situations.
Trotsky too, wanted that for the Russian people. He hoped to see Russians profit from their work. His function in the beginning was as a military leader, but really, his visions were for people.
Napoleon, not very gifted with speaking to the animals, had to use Squealer to often further articulate his purposes. Napoleon also just got rid of animals who didn't fulfill his purposes. He also killed animals just because. Stalin, likewise, was not a prolific speaker, but had a purpose of either using people or killing them.