You have to be calm and having al the patience... I think doing every day some work and rewarding him if he does well that exercice it will work! But remember! A LOT OF PATIENCE!
My mare did this as she also has a huge past for a 3 year old, if you have the facilities a round pen will do, he needs to learn to respect you, if he's aggressive he's learnt that by being like that gets people away from him so never back down as horses can sense the slightest weakness, a lot of free lunging and natural horsemanship such as sending him away in the round pen then asking him to stop and respectfully face you, these are the first steps I would take :)
Do a lot of ground work and get him to trust you 110% before you slowly start to work him