I think that this is an interesting question because the humans don't get a great deal of attention in the novel. One human who plays a big role in the narrative would have to be Mr. Jones. In many respects, he inspires the entire revolution because Old Major uses him as the representation of the evil nature of human beings. Jones' cruelty to the animals as well as his own inability to control them, in terms of getting drunk and forgetting to feed the animals, becomes the basis for the revolution as the vision that Old Major was able to articulate in the first chapter is the basis for revolt in the second chapter. In these domains, Jones plays a vital role. Mr. Frederick would be another human who plays an important role in the novel as he strikes a deal with the animals only to violate it. In the end, the humans' cruelty and lack of decency becomes the rallying cry for the animals, and, ironically, something that Napoleon himself embodies.