Rats behavior keeps biting?

I have 2 male rats now 6 months old, I handled them since they were 6 weeks with no problem. In the last 2 months 1 of them has become very nasty, as in launching himself at the cage when some one goes to it snarling and squealing, if you try to handle him he will bite or attack anything I put in the cage to try and catch him. He is the dominant male and always tries to attack the other one but not to the point of bloodshed. They both were very good when being handled but this 1 wants nothing to do with humans, he eats a varied diet including veg once a week and various treats. I don't want to get rid of him but it's becoming impossible to even clean the cage