Like Stalin, Napoleon becomes dictatorial, demanding that people serve him well. He creates propaganda, tainting the truth to suit his aims, just as Stalin did. When others doubt him, and they challenge some of the issues, Napoleon has the vicious dogs attack the offender. Others are forced to confess to actions they have not committed and are done away with, just as Stalin had millions of his own people killed. Anyone who lived feared and dreaded him because of his police terror, just as the animals live in fear and dread of Napoleon and his wild dogs.

Like Stalin, Napoleon had several allegedly disloyal animals, including many who had been important in the revolution, executed. Several of the hens, who did not want to give up their eggs, revolted and were executed, as were several pigs who  confessed to being sympathetic to Snowball. The first evoked memories of peasants who were executed because they did not want to give up their crops to meet quotas, and the second may remind readers of officers and loyal communists who perished in some of Stalin's purges.

One major similarity is in the way that they both created cults of personality around themselves.  Napoleon did this by using Minimus to make up things like the hymn to how great Napoleon was.  Stalin did the same thing by setting himself up as the father of his country and the source of all good things.

Napoleon, like Stalin, reallly tries his best to create a totalitarian regime on the farm.  He wants complete control and achieves it through various strategies, like eliminating dissent, using fear to suppress and control his enemies, and controlling information, through his own style of propaganda.

Another similarity is that like Stalin, who concluded a non-aggression pact with Nazi Germany, Napoleon makes a deal to sell timber to the animals' sworn enemies, the humans. Like Stalin, Napoleon paid dearly for the mistake, as the humans gave him counterfeit money and launched an attack on the farm. 

These two are very much the same.  Perhaps the clearest connection is between Napoleon's relationship with Snowball and Stalin's with Trotsky.  Stalin felt threatened by Trotsky and had him exiled.  It's also important to remember that Stalin conducted purges of anyone who he saw as a threat (like how Napoleon has the dogs kill various animals).

One of the most memorable correlations between the allegorical character of Napoleon and the historical person of Stalin is the treatment of political enemies. In Russia, Stalin imprisoned or killed many of his political enemies. This campaign was known as Stalin's purges. In Animal Farm, Napoleon first has four pigs executed for treason. After this, other animals begin to confess to crimes that they apparently did not commit (this happened in Russia also) and are also executed.