Besides Napoleon, what other animals illustrate the abuse of power?

Besides Napoleon, Squealer also illustrates the abuse of power. Unlike Napoleon, who primarily uses fear and violence, Squealer abuses language in order to maintain power over the other animals.
To see an example of this, take a look at chapter 3, when it is revealed to the animals that the pigs have stolen the milk and apples for their mash. In this example, we see Squealer abusing language in order to justify this unfair distribution of the farm's rations:

Milk and apples (this has been proved by Science, comrades) contain substances absolutely necessary to the well-being of a pig. We pigs are brainworkers. The whole management and organisation of this farm depend on us...Do you know what would happen if we pigs failed in our duty? Jones would come back! Yes, Jones would come back!

Here, Squealer uses a combination of false statistics and scaremongering (by threatening the return of Mr. Jones) to maintain the pigs' better rations. Squealer is able to do this because he is more intelligent and confident than the others. By overwhelming them with false statistics and fear, they are powerless against his arguments and about this unfair situation, more generally.