Welcome Crankykid, My son was exactly like this starting around 1 1/2 old getting worse as the years went on. The defiance, violence, biting himself and threatening us was added to that. Insane and wiped covered the questions, what to read and who to go to. Have you brought this up to his Pediatrician? Its been years in the making on how to handle my son, seeing different types of doctors etc( he has calmed down from that overall and we have learned some of his triggers as some we never know). Be consistent, not too many choices, with two if he needs to chose something. Dont bend rules and punishments as they learn to keep getting their way. Simple punishments, nothing to harsh but enough to grab his attention. Pick your battles as I was told and read. Try to keep him busy, see if you can get him to talk on how hes feeling about things when hes calm and happy. ( of course he might not be able to explain how he feels due to his age or not understanding how to explain or how he feels- the psychiatric doctors can help with talking with him if need be) Rule out any possible allergies, health issues and surroundings as well. Oh, as long as your son isnt hurting himself, just let him tantrum, my son also got worse when we tried to calm him.
And,not everything will work for all of our kiddos,this is whats helping me with mine from the wonderful people here, books, parents, strangers, doctors of various kinds of course!!!. I wish you luck and give you many hugs!