If he behaved well until 4 years ago, is it possible he had some sort of trauma or abuse, potentially at the hands of a relative or caretaker? The sudden transition seems to be a symptom of something traumatic or some sort of other issue, and he may need some serious help.

So, for nearly half your life, he's been an asshole. Unless you start disciplining the little bastard, he's going to become a big problem -- maybe even like those assholes in Buffalo and Uvalde!

This has trauma written all over it. You need to figure out what, and better late than never.

Please listen to him and take him to get professional help (and not the medication-only kind). This is a strong sign that there is something wrong (as others have said, very likely something traumatic happened) and he is suffering. And research (also my personal experience) seriously debunks the so-called power of roughness and discipline, please don't listen to the other guys who suggest just that, that causes more harm than good, especially in a case like this. I'm rooting for your family.

Kids act how they’re allowed to act. I have an 8y/o nephew. He was also great until he was about 4. He is a terror now. He has never been abused or experienced any trauma (since that’s what so many people here seem to be stuck on as a reason) He is an only child and his parents can’t seem to tell him no. He gets whatever he wants, whenever he wants it (kid has an Amazon wishlist that he knows how to add to so his parents - my bro and my SIL - know what he wants them to buy him) Point being that he has had so many issues at school that they have him in therapy now. So without any additional info..I kinda have to say you may actually be at fault here. Sorry :(

As someone who used to work with children who had behavioral issues, it's most likely one of the three most common factors. #1 The child went through some sort of traumatic experience and has PTSD. #2 They have some sort of developmental disability such as autism or a learning disability. #3 They have entitlement syndrome also known as their a spoiled brat. These are your most common issues with children that can cause behavioral problems. Of course there are other factors like for example, it could be a brain tumor or severe mineral or nutrient deficiency but those are much less common issues. Either way it's time to go see some medical professionals both mental and physical and determine what the issue is.

Good God why don't you have this child in therepy? Obviously something happened and he's crying out for help.

I was like this after 4th grade. 30 years later and I still deal with depression and asperger’s daily. Reach out to boys town national helpline. They can help. He needs some extra care, but if jhe was a nightmare like me, with the right choices and help, he can turn out ok!