Have your vet check for ulcers!
I use these! Not the exact brand, but you get the idea
Are you sure that this behavior doesn't come from some pain? If he started getting angry recently, maybe you should show your horse to a veterinarian or an osteopath.
If it's not coming from a pain, maybe just let him be angry as long as he doesn't bit or hit you. If he does, you need to be ferm with him so he doesn't get aggressive.
Good luck :)