Actually I agree with JustDressageIt. I think the first thing a horse should always know is how to do a one-rein stop. Starting at the walk, then trot, then canter. Take your hand around and plant your fist on your hip, don't let go until rhe eleases the pressure on the bit. (watch him carefully for ANY sign of giving to the pressure) You may walk around and around in circles or just stand there for several minutes with his neck bent.. but they will start trying different things to see what will let them straighten back out: moving their haunches over, pointing thier nose up and down, etc and finally chewing and licking, then pointing their nose closer to you to let go of the pressure. As soon as he does that, release the rein and give him a big pat. It's 1) an emergency stop (he'll know it as a cue if you teach it to him before an emergency arises) and 2) since you're teaching him to release pressure it's a great first step on teaching him to submit to the bit and one day go on the bit again. You must keep your hand fixed in one place to properly teach him, and keep it low (on your hip) or there is a danger of flipping him. Remember to sit square and deep in your saddle.
So what's the history on this horse? Sounds like he's not trying to necessarily be bad. More clueless so he's ignoring your cues because he doesn't know they're cues. You may just have to start him from the very beginning and just forget where he was before and what he knew before. You really can't compare! Pretend like he's completely unbroke and teach him every little thing step by step. I do think restarting a horse takes less time then starting from scratch.