Boxer is the hardest-working animal on the farm in George Orwell's Animal Farm, and he represents the common man in this novel about the Russian Revolution and Stalin's rise to power. In other words, if we watch what Boxer does and how he is treated, we can see how the average person was treated under this kind of dictatorial regime.
From the beginning, Boxer not only does more work that any other animal on the farm, he also does his work willingly. While he is not the brightest animal on the farm, he is also not the dumbest; every time he begins to question his leaders or what he remembers to be true, he contemplates seriously and then chooses to believe the best about them. He does what he is told and harms no one. Even when he inadvertently hurts one of the men who come to take back the farm, he feels miserable thinking that he might have killed a man, even in battle. Boxer is a noble, hard-working horse who never deliberately hurts any other animal on the farm. His determination to "work harder" ensures that things get done on the farm, and this does benefit the other animals despite the fact that the pigs benefit most from anything that is produced on the farm. His motto "Napoleon is always right" does create a dilemma, at least, for the animals, as it becomes clearer that Napoleon is not always right. His is not a completely blind trust of Napoleon, but it is close. While it is true that at some point Boxer could have led the charge to oust or overthrow Napoleon, once Napoleon has his dogs, anyone who tried to revolt would have been killed.
Despite that, there is one thing he does--actually, it is something he does not do--which might be seen as harming his fellow animals, though he never realizes it. In chapter seven of the novel, Napoleon oversees a horrible time of confession (mostly false) and slaughter, a time known in Russian history as the "blood purges." There is a moment that might have changed everything for the animals, but Boxer misses the opportunity.
To the amazement of everybody, three of [Napoleon's dogs] flung themselves upon Boxer. Boxer saw them coming and put out his great hoof, caught a dog in mid-air, and pinned him to the ground. The dog shrieked for mercy and the other two fled with their tails between their legs. Boxer looked at Napoleon to know whether he should crush the dog to death or let it go. Napoleon seemed to change countenance and sharply ordered Boxer to let the dog go, whereat Boxer lifted his hoof, and the dog slunk away, bruised and howling.
This is the moment which would have changed everything. If Boxer had realized his own power, he would have killed the one dog which would have intimidated the others enough to allow for a new rebellion. Even then, Boxer could not have overturned the power structure on the farm unless all the other animals had been ready to stand with him, and we have no clear indication of that.
It is true that Boxer should have done more questioning of Napoleon's authority, which rather sets the tone for the other animals on the farm; however, none of the other animals seem inclined to go against authority, and those that do are promptly killed. Boxer represents "everyman," and he trusts more than he should; however, it is hard to say that he is more responsible for the animals' circumstances and future than Napoleon and Squealer are--and if he is, he certainly pays for it with his own life.