Most of the named characters in Animal Farm are allegories for real people who lived and died in the Russian Revolution and afterwards. Old Major, the creator of Animalism, represents Karl Marx, the creator of Communism. Napoleon and Snowball represent Joseph Stalin and Leon Trotsky, who were instrumental in forming the revolution; as in real like, Napoleon drives Snowball from the farm to keep personal power. Squealer and the dogs are the propaganda and military arms of the government, respectively; Squealer spends his time convincing the animals that their hardships are actually good while the dogs kill anyone seen as subversive.
Napoleon was a large, rather fierce-looking Berkshire boar, the only Berkshire on the farm, not much of a talker, but with a reputation for getting his own way. Snowball was a more vivacious pig than Napoleon, quicker in speech and more inventive, but was not considered to have the same depth of character.
(Orwell, Animal Farm, msxnet.org)
Snowball, like Trotsky, genuinely believed that there could be a system in which each animals works to their ability and each takes according to their need; Napoleon, like Stalin, understood that the system was inherently unworkable and so worked towards amassing personal power instead. In this fashion, the characters of the novel represent the real people of the Russian experiment with Marxism, and show how those experiments ultimately led to a worse situation than the one they rebelled against.
Old Major represented Karl Marx. Old Major though of the concept of annimalism. In our world, Karl Marx thought of the new concept of communism.
Mankind represented the royalty in Russia. Mankind represented the Tsar's family who only enjoyed themselves. In the novel, Mr Jones enjoyed himself and drank, forgetting to feed the animals.
Napoleon represented Joseph Stalin. He was brutal and was the second leader of the Soviet Union. Napoleon chased Snowball out just as Joseph Stalin chased Leo Trotsky out of the Soviet Union.
Snowball represented Leo Trotsky. He was the first leader of Annimal Farm and like Trotsky, who first led the Soviet Union before being expelled like Snowball.
The horses represented the workers. Specifically, Boxer represented the people in Soviet Union who believed that the communist party was always right. Boxer motto is " Comrade Napoleon is always right". Mollie represented Russia's upper class who escaped to othercountires when communism tookover Russia. She, like Russia's upper class, escaped to a nearby farm.
The dogs represented the secret police. Russia had a fleet of secret police called the NYKD initially. Everyone feared them. Like the NYKD, the dogs instilled fear in everyone and made sure that there was no opposition towards the ruling party.
Squealer represented propaganda. He helped the pigs to spread their message to the animals. Just like how the communist party used propaganda to spread their message to the people.
During the time he wrote this book, Russia was currently facing Russia Revolution when people revolted against the Czar family. This book is an allegory and Orwell wanted the people of Russia and the world to know that revolutions do not work.