In Animal Farm, Boxer's work ethic and loyalty are his strengths.
Orwell makes it clear that Boxer works harder than any other animal on the farm. His physical strength is distinctive: "Boxer was an enormous beast, nearly eighteen hands high, and as strong as any two ordinary horses put together." When it comes to work, Boxer uses his strength towards collective aims. This can be seen in the first harvest, in the building of the windmill, and defending the farm against external threats. His strength is one of his attributes.
Boxer displays an intense sense of loyalty to the farm. In the opening chapter, he and Clover gingerly navigate the smaller animals so that he won't hurt them. He continually shows his loyalty towards the revolution with his efforts and his loyalty to Napoleon. Boxer's mantras of "I will work harder" and "Napoleon is always right," show his loyalty. Boxer is honorable in how he remains loyal and does not ask questions. Orwell sees this as a source of strength and undeniable weakness. Boxer is so loyal that it never occurs to him that the pigs care for power more than they care for the aims of the revolution. Boxer's loyalty towards the other animals is ultimately shown in the way he works, even as he gets older, to help the farm, something that eventually ends up killing him.