What are positive and negative actions of the pigs of the Animal Farm?

In the beginning of the book, the pigs do many positive things for the animals. Old Major, the boar who dies before the animals revolt, offers them his vision of a world of animal unity and cooperation without the need of human masters. Snowball, before he is driven off and exiled, provides responsible leadership that stays true to the ideals of the revolution. He writes the Seven Commandments on the wall of the barn, proposes building the windmill, fights bravely against Mr. Jones, organizes the animals and studies farm management to help the new society thrive. 

On the other hand, Napoleon uses his superior intelligence and cleverness to amass power for himself and begins to alter the animal's vision of a utopic society in which all share equally in the fruits of their labor to one where he profits. Napoleon surrounds himself with vicious dogs who tear out the throats of animals Napoleon decides are enemies. Napoleon engineers the society so that he and his cohort commandeer most of the benefits of the hard work and sacrifices of the other animals. Napoleon changes the slogan that says all animals are equal to read that all animals are equal but that some are more equal than others. He violates all seven of the Seven Commandments until finally he is indistinguishable from the human masters.