Timid dog

That sounds like something happened to it. Most likely it will never get much better. It could possibly be used for breeding if it has good genes. But I would not give up. I have got a couple dogs over it but it took lots of work. It is all about body language, eyes, and more. Get low, turn your head to expose your neck it shows you don't want to fight, do not make eye contact it can be a sign of aggression, take small steps. Work to just get close and do not touch for a week. Then just a casual light touch occasionally for a while then a small pet. You have to work on building trust. But watch out sometimes they may suddenly turn aggressive if you push to hard. Better to go too slow than too fast.