One group of characters that represents both its animal and human characteristics is the group of dogs that Napoleon gathers as his guards. Dogs are well known as loyal animals, and they protect their masters without question. In Animal Farm, the dogs protect Napoleon and do his bidding without any question. When Napoleon orders that they kill other animals, they carry out the task because their master ordered it. The dogs' human counterpart (if looking at the novel from an allegorical perspective) is the KGB, a group of secret police employed by Stalin who also did his bidding without question. The police exhibited the same sense of loyalty to Stalin and the State as the dogs do to Napoleon.
I would say that Boxer is a character that represents the essence of the working masses or the individuals who are powerless over their fates. They have no choice but to place their trust in the government. Boxer does whatever needs to be done and commits himself to working harder and with more diligence in order to fulfill the government's wishes. In the end, he is led believing that he is helping the government, the state, but ends up sacrificing his own life in the process. Boxer represents the trust that people place in government, and the lack of questioning it can result in their own personal and professional demise. When Boxer dies and when it is covered up in such a deceptive manner, it reflects the trusting aspect of human nature and how this can be so easily twisted by those in the position of power.