Mickey's aggression is getting pretty bad

So Mickey and I have gotten to be very bonded and he enjoys being around me. He has, however, gotten to be very aggressive around anybody else. He doesn't allow anyone to touch him, be close to him (or me). It started as him just moving away when people walked up to him. He wouldn't show any aggression but I could tell that he didn't like other people. But now its actual aggression. He has bitten my dad, lunged at my friends. Just last week he was sitting on my shoulder, a friend of mine walked past me really closely and Mickey tried to fly off my shoulder to get my friend.
When I first got Mickey, he wasn't aggressive. He just didn't trust me. So I never thought of Mickey as aggressive. I've tried to reward Mickey whenever people come over and I try to make it a really pleasant thing to have other people around. He is not having it! He doesn't care, he wants them gone. How can I change this?
IDK much about Mickey's background. all I know is that for 12 years, he's had one owner and he died. So I'm not sure if maybe these overly aggressive tenancies stem from something that happened early in his life

Sounds like you need to do some more reading on how best to socialize Mickey, rather than just trying to bond with him.....

Without proper socialization, people and/or your friends are not going to want to come around anymore and you're the only person that can stop this behavior. Here are some videos that may help:

My Parrot Bites?What Can I Do?

[ame="https://www.youtube.com/watch?v=GdwI5f0-sJc&utm_source=getresponse&utm_medium=email&utm_campaign=windycityparrot&utm_content=Free%20Bird%20Training%20Videos%20-%20Aggressive%20Biting%20Birds%20%26%20What%20Not%20To%20Do%20"]How to Train a Parrot : How to Train Parrots to Stop Biting - YouTube[/ame]

[ame="https://www.youtube.com/watch?v=-fOR83fBsP4"]How to Train a Parrot : The Don'ts of Training Parrots - YouTube[/ame]

[ame="https://www.youtube.com/watch?v=Taov-BD4AOA"]Secret to stop small birds from biting! - YouTube[/ame]

[ame="https://www.youtube.com/watch?v=KrhSgcHkKXA"]The Solution to Stop Your Parrot From Biting ! - YouTube[/ame]

[ame="https://www.youtube.com/watch?v=1K_lRwaGj2w&utm_source=getresponse&utm_medium=email&utm_campaign=windycityparrot&utm_content=Free%20Bird%20Training%20Videos%20-%20Aggressive%20Biting%20Birds%20%26%20What%20Not%20To%20Do%20"]Parrot Training: Pet Bird Tameness ... Touching How to train a parrot - YouTube[/ame]

[ame="https://www.youtube.com/watch?v=r52GXrsimCo&utm_source=getresponse&utm_medium=email&utm_campaign=windycityparrot&utm_content=Free%20Bird%20Training%20Videos%20-%20Aggressive%20Biting%20Birds%20%26%20What%20Not%20To%20Do%20"]Moe, Retraining An Aggressive Blue and Gold Macaw - YouTube[/ame]

[ame="https://www.youtube.com/watch?v=jbCw_O7cll0"]Parrot Aggression: Dealing With One-Person Birds - YouTube[/ame]

Good luck.....

It seems that he is being protective of you. I would suggest putting him on a stand, leaving the room, then having someone else (who is confident and comfortable with him) come in and do some exercises with him and give him lots of treats. Remove yourself from the equation as much as possible so that he gets comfortable with others separate from you then slowly start putting yourself back into the equation by doing things like just sitting and talking to someone else while he is in his cage completely ignore him unless he is absolutely calm then reward him. Greys are stubborn and very quick to over-bond and be over-protective.