I had a tow truck driver who had a Ph.D in mechanical engineering. He worked for an engineering company for a few years before he decided to move back to the mountains. I learned so much about control theory riding with him in the cab of his truck.
He rarely told anyone his credentials. Most people thought he was just some old man. I watched parents and teachers be rude to him, but he'd always smile and be polite. Some of us used to help him from time to time. He was very kind and would always listen to our kid-sized problems while we worked.