As we know, Animal Farm is a fable based on an allegory of the Russian Revolution. In that way, each character represents an important historical figure. Old Major is Karl Marx.
Old Major is the old boar whose vision of Animal Farm starts the revolution. Old Major has a dream, and gathers the animals around to hear it. He describes an idealistic place where animals are their own masters, and everyone has enough to eat and a small share of the workload.
Karl Marx was actually a Prussian (German) philosopher who wrote around the turn of the 19th century. He rejected capitalism. His equivalent of Old Major’s dream was Das Kapital. In it, he describes a system of communal wealth and sharing of labor. He believed this would be a better and more stable system, able to take care of all its people. As you can see, this is very similar to Old Major’s ideas.