Getting him fixed would be the best thing, those little things can make all the difference in the world on a dog or cat's behavior.

also, you could make him an outside cat to give him a means of burning off his energy. my 2 cats used to fight connstantly, and 1 of them actually tried to get us mad just for a reaction lol, but once we started letting them go outside they've been acting just fine and rarely fighting anymore.