The loyal cart-horse whose maxims, I will work harder and Napoleon is always right, built the regime that sold him to the knacker.
Documented
The working class in one horse
Boxer stands for the loyal labor of the revolution: the Stakhanovite workers who built the Five-Year Plans and were consumed by them. In the book he is sold to the glue boiler when his strength fails; the pigs deny it; the money buys whisky. Orwell confirmed the equine cart-horse reading in his own notes.
Assessment: Documented: textual role, confirmed by Orwell's prefaces and letters.
Stories
The good man who enables evil
The modern citation: 'Boxer' as shorthand for any decent, hardworking person whose trust funds a corrupt machine. He appears in op-eds about unions, armies, and electorates, always as warning, never as insult.
Assessment: Stories: as archetype he outgrew the USSR within a decade of publication.
Interesting claims
The strength that refused doubt
The harder question the fable asks: Boxer could have stopped everything. The other animals defer to him; one word from the horse and Napoleon falls. His tragedy is not weakness but a refusal to think that he chose, twice, as a maxim. Complicity written in muscle.
Assessment: Interesting: the novel plants this explicitly, his kicks could have ended the dogs; readers who blame only the pigs miss the assigned homework.
Sources and further reading
George Orwell, Animal Farm (1945), chapter 9, the knacker's van scene
Orwell's letters on the working-class reading of Boxer
Bernard Crick, George Orwell: A Life (1980)
Worth asking
Is blind loyalty a virtue the system rewards, or the fuel the system runs on?