I've had him bite me one time that broke the skin, but I don't think that was his fault. I was handing him a treat as I left the house, and I had fingernail polish on, which I never wear because of work, and I handed him the treat kind of sideways, so I think he thought my fingernail polish was what he was supposed to grab. I didn't yell at him or get mad at him, but I've heard him go "Ow!" a few times since, lol.
As for his history... I don't have much on it. As far as I can tell, he never had an 'up' command and was never even allowed to step up... he was just picked up. He has issues with new perches of any size. He freaks out and will completely avoid that part of his cage. After a couple days, I just took it down. I don't want him to feel unsafe.
I have a friend that has scratched his head while he was sitting on his swing. And he gives me the same feather fluffing, head down treatment, but he bites when I try. I know he wants attention because I've been around my mom's Macaw, and have seen the same behavior. I'm just afraid of getting hurt.
I'm more than willing to give him all the time he needs to adjust. I haven't shut his cage door in weeks now, unless his safety demanded it for a few minutes. He has tons of toys to play with and I rotate them and replace them when he seems to get bored. If he doesn't like a toy, I simply take it back down. We've made a game of cleaning out his cage. I use a damp towel to wipe it down, and this agitates him, so I hold it up to him and he bites it and tugs as we both say "arrrhh". He loves to make that sound.
I love this lil guy, and I want to make sure that he's happy, and he seems to be a tad lonely. He hangs on the edge of his cage at night and watches us go to bed as I say "Goodnight, Gandalf". His wings are away from his body, and he bobs his head and flaps just a tiny bit like he wants to go too. He even flew down to my bedroom one night, but I can't pick him up to take him down there to sleep on his perch. I just want to do what's right for him.