The Doctor comes from a planet called Gallifrey: he is a Time Lord. His name has never been said on the show. He knows what it is but he chose the title Doctor to go by. If I remember rightly even his wife (River Song) doesn't know his name. Once Clara said it wasn't important what his name was because he goes by the Doctor and that is what he is: a healer, a helper, and he doesn't need any other name.
Oh, and I know you probably just called him "Doctor Who" so we know who you're talking about, but that isn't his title. It's simply "The Doctor", or "Doctor" when to his face. In the first few series the credits listed him as Doctor Who but never in the show that isn't his title.
As for who knows his secret, in real life: nobody has said they do so it seems that nobody does. Due to the nature of a long running show with multiple writers the current showrunner can put his name in whenever he wants. I don't think he actually has a cannon name because that's part of the characterisation: no showrunner has ever included a name for him.