What are the individual roles of the pigs in the book "Animal Farm?"
Well, it looks as though, based on your examples, you are already on your way to answering the question! There are not a lot of pigs who are known by name in the book so it is not a hard one to research:
NAPOLEON: Napoleon role is as a authoritarian figure on the farm. He is the mastermind behind the pig's ability to control the farm. If you are considering the Russian Revolution, Napoleon represents the "Stalin." In the end, he is the craftiest of all the pigs.
SNOWBALL: Roughly the "Trotsky." He is intelligent and passionate about his ideals and the direction he feels the farm should take. He believes in the ideals of the revolution and acts courageously in battling the humans. Unfortunately, though he is intelligent and has the best intentions for the animals on the farm, he is not nearly as crafty as Napoleon and therefore is destined to be "driven out." He, too, is not without flaws...he quickly accepts the idea that the pigs are superior to the other animals.
SQUEALER: I wouldn't call Squealer "the liar." He is a manipulator of information, not a pathological fabricator. He shows how, using rhetoric, half-truths, and "spin," it is possible to control people. His role on the farm is really as minister of propaganda.
OLD MAJOR: The original swine. He is representative of kind of a mix between Lenin and Marx, in real life. His role was as the visionary of the revolution. It was his ideas that started the whole ball rolling. He is the ideological "heart" of the rebellion. He is an inspiration. Interestingly enough, Old Major is the animal who, aside from the bird, has suffered the least on the farm. As a "prize pig" he has lived a pretty spoiled life, yet he is the one who thinks most of the injustices found in the farm.
MINIMUS: His role is kind of minor. He seems to work with the "propaganda department" and is the one who comes up with the "new and improved" anthem for the farm.
I think that is all the oinkers. Mmmm....bacon.