Hi and welcome.
First, congrats! I'm so glad this poor little one is with you. It's very clear to be that he was grossly neglected and very possibly just stuck in a cage. Be patient, give lots of TLC and he will come around...but he will be scared to trust, obviously.
Second though, PLEASE call your local humane ass'n and tell them about the kind of shape he was in and that you believe there are a LOT of other animals in this horrible person's care - please help those other dogs!!!