Answer:
Old Major - Karl Marx
Napolean - Joseph Stalin
Snowball - Leon Trotsky
Squealer - Soviet propaganda newspaper Pravda
Boxer - exploited hard workers
The Sheep - the easily led masses
The Dogs - the secret police
The Hens - the kulaks (people who didn't coorperate)
Moses - the Russian Orthodox Church
Benjamin - the Jews and others, who did not like the change any more than before and were aware of corruption, but did not act, because they saw that corruption and cruelty would always happen
The Cat - The lazy people who go along with Communism, because it means they get fed, without having to work
Mollie - The white Russians who were treated well under the Tsar, so preferred it before the rebellion
Clover - The workers' wives
Not animals, bu still characters:
Mr. Pilkington - The Allies (mainly Britain)
Mr. Fredrick - Germany
Mr. Jones - the Tsar