There are alot of things you can do. Does time out work? My younger one HATES time out. We have him sit on the bricks of the fireplace without toys and we set the timer. Our older one we have write lines, as in "I will not hit my brother" 10 times or whatever. You really want to nip this in the bud.
Try talking to him about his anger or having him draw pictures of how he feels and why.