Jen, I know I am late responding. Hope you are still following. I agree with the others - leash and medical checkup. Be sure to have his thyroid checked. Aggression can be a symptom of a thyroid issue. Definitely keep him leashed. It sounds like resource guarding to me. Resource guarders will guard food, toys, space, etc. Dogs can be reconditioned. It takes work and time. Meanwhile, you need to keep everyone safe. A leash will keep him under control and enable you to move him away from whatever he is guarding. Crate him, or put him in another room, when people are visiting.
What signs did he exhibit before the bite? You will have to become an expert on your dog and learn to read him. There are always warning signs that a dog is uncomfortable about something - body tension, tail between legs, lip licking, growling.... You need to watch for those signs. Yelling at a resource guarder, or giving any kind of harsh correction will do nothing - probably make things worse.
Really up his obedience training. Hand feed him and make him work for his food. Sit! (food), Down! (food), Come! (food). Then incorporate some tricks - High 5! Beg! Use the hand feeding as a time to teach him watch and gentle. You want your dog to focus on you. Tell him watch. Hold a piece of kibble near your eye. He will look at the food, but will also make eye contact with you. As soon as you have eye contact, "Good Boy! Watch!" Before giving him the food, say, "Gentle". If he takes it gently - "Good boy, gentle." *Note - Gentle should be said in a soft, calm voice. If his teeth catch your fingers, "NO TEETH!" And mean it. Before long, your dog understands gentle and no teeth. He will understand what it means, to be gentle with a puppy, or a child. He will understand that touching teeth to human skin is bad.
Another exercise that is very helpful, is to have your dog sit next to your chair, while you sit on his leash. Allow him enough leash to lie down. Don't look at him, or talk to him. Work on your computer, or read a book. Ignore your dog. Eventually, he will lie down. Do this for 30 minutes every day. It teaches the dog to relax. He will start to lie down sooner each time. Changes don't happen over night. You will have to watch him to see what causes him to react. He needs to be desensitized to those things. Obedience and these exercises will help to build a bond between you and your dog. You need mutual trust and respect.
Natty Boh was a terrible resource guarder when I got him. He had to learn that I always gave, never took. I would trade up, for something better. But I never snatched things away. When I gave him something, it was his. If I asked him to give it back, there was a reason - not just because I could. Natty Boh is 10 years old now and he is a very good boy. He still has a lot to say about things, but it's been quite a few years since he has bitten anyone.
I hope you see this and I hope it helps. Definitely get that checkup. Dogs are stoic. They don't always show their pain. We might miss when they are hurting, or sick. That is definitely your first step.
All the best!
