Rescue Dog Afraid of Owner?

I have a Belgian Malanois-Whippet mix. Since I rescued him he is still afraid to let me help him. My dog is still uncertain of me. He looks afraid when I go to pet him sometimes. He is a character. He hates dog food and makes me give him my food or he pouts, literally. He dictates where we walk. I don't mind that though it's his walk. But his frightened disposition when there's no threat is sad. And he wants to kill the mailman. He has been massed 3x for this same aggressive behavior only to certain aggressive type people. He bosses me by using his tail and stepping on my toes. Ugh. He is is close to 12.