Griffin used to be pretty aggressive, he attacked me and would've chased me if I ran. But, I never ran from him and chased him periodically, so he's no longer aggressive.
I have a formerly aggressive rooster called Griffin. All I did to stop him from being aggressive was chase him when he tried to dominate me, walk straight toward him so he had to move away, and hold him down when he was being aggressive. It worked perfectly, he is completely non-aggressive now.