Animal Farm is an allegory of the Russian Revolution. This means that the events in Animal Farm are meant to directly represent the events of this revolution.
When looked at in this way, it becomes clear that Farmer Jones represents Czar Nicholas II, the head of the old Russian regime, because they are each an established head of power. The animals represent different radical figures in the fight against Farmer Jones and other opposing forces in this struggle. For instance, Moses the raven is a favorite pet of Farmer Jones. Moses represents the Russian Orthodox Church. The church and Moses both act to try to talk down revolutionaries with false promises in order to protect established power structures. Old Major, the head of the revolution, represents Lenin and Marx. Old Major has the ideas that get the other pigs riled up to change their situations, much as the writings of Lenin and Marx began to do in Russia.