My horse chases other horses away..?

My horse is aggressive towards other horses, wether in the pasture or in the barn. I was watching him in his stall and he put his ears back and tryed to bite the horse in the stall next to him.He kinda runs at the horse. In the pasture he chases of horses in his way. He keeps chasing them off. All the horses are scared of him. How can i make him stop this?