Boxer was a loyal, hard-working, and caring member of the animal society. Here is how we see each at work:
Loyalty: Regularly Boxer would say "Napoleon is always right." This shows his commitment to his leader. Moreover, he would rise early and work longer on the windmill because he had the strength to and he knowing so, he did this to relieve other animals who were weaker from more work.
Hard-working: Boxer also regularly said, "I will work harder." This maxim was a true statement reflecting his commitment and he worked himself to death. After hauling for years, his body aged and finally gave out. The commitment to work more hours of the day at each announcement of the need for more work demonstrated this trait as well.
Caring: I think Boxer saw a better future and believed in the false visions given by Snowball and Napoleon. I believe this because of his loyalty and hard work. I think he saw a better life for his friends.
In Ch.6 Orwell describes in great detail how the animals struggled to build the windmill. Large stones had to be hauled up a steep slope and then allowed to roll down to be broken into small pieces. This laborious process, was accomplished mainly by the unrelenting efforts of Boxer:
"To see him toiling up the slope inch by inch, his breath coming fast, the tips of his hoofs clawing at the ground, and his great sides matted with sweat, filled everyone with admiration. Clover warned him sometimes to be careful not to overstrain himself, but Boxer would never listen to her. His two slogans, "I will work harder" and "Napoleon is always right,"seemed to him a sufficient answer to all problems."
He represents the common people of Communist Russia who were exploited by Josef Stalin and his henchmen.