Benjamin, the donkey, claims to have lived through many changes in his life, and is pessimistic that the revolution will foster real change. He claims that everything remains the same, no matter how drastically they seem to change, and that there is no point in fighting or struggling because the status quo will always return.
Only old Benjamin professed to remember every detail of his long life and to know that things never had been, nor ever could be much better or much worse -- hunger, hardship, and disappointment being, so he said, the unalterable law of life.
(Orwell, Animal Farm, msxnet.org)
In this sense, he represents George Orwell, who was pessimistic about world events and their larger meaning. Orwell didn't believe in Utopian ideals, from any political point of view, and thought that people would continue to work hard for little reward no matter who was in power. Benjamin, through his stolid nature, does not make friends or enemies, and so is not targeted by Napoleon's dogs. Benjamin's claim to remember all the details of his life also represents Orwell's profession as a writer; although he does little to put forth his point of view, Benjamin has chronicled the history of the farm in his head.