Napoleon (Animal Farm)

Napoleon is the main villain of George Orwell's famous book Animal Farm - he is a fat, greedy pig who turns the farm into a dictatorship parallelling the events of the Soviet Union (which the story was based on)

Napoleon helped to overthrow the humans that had been oppressing the animals in the farm with help from fellow pig Snowball but soon becomes extremely corrupt and cruel - disposing of animals that displease him and adopting policies almost identical to those used by the humans they had fought against.

In the end of the story Napoleon and his fellow pigs (minus Snowball, who ran afoul of Napoleon and disposed of) are so corrupt that the other animals can no longer tell the difference between the pigs and the humans.