I think I've seen you here on AB for a long time (although irregularly newtron... I guess I dind't realize you are in the U.S. (with a name like that, you must be near Alamogordo!).
At any rate, you don't say, but I assume the "he" horse is a gelding? If not, that can certainly be one of the behavior problems. If he has been gelded, I would suggest a really good work out a couple of times a week. By that I mean a good walk, trot, canter for at least two hours or more. If you can get him to the country and ride him in the hills, so much the better.
Another, simple, but effective tool to use in changing his attitude is to show up each time with an apple in your jacket pocket. A horse has a keen sense of smell, and apples will get his attention. He will approach you and probably nuzzle the pocket area. Let him do this for a few minutes and then have him eat it out of your hand. Again, try and be consistent and have the treat each time you go out to where he is. This let's him know you can be trusted.
This time of year, especially in your part of the country, he still has his winter coat on. This will soon begin to shed and becomes uncomfortable and itchy. Find a good curry comb (I like the ones with a wooden handle and about three rings of spring steel with teeth lookin things.) Start on his shoulders (they really like that) and then work your way around him. As time goes on curry his belly and down his legs. (Don't use a lot of pressure on his legs and be careful of the "corks" on the inside of all legs. This, again,will engender trust.
Having said all that, be a bit leary of him... he may try to bite or possibly even kick, until he's comfortably used to you.
What kind of bit are you using in the bridle? Just want to make sure he's not tender mouthed.
Best of luck!