In common speech, oneself. As in, "I am in my own skin, at last."
My own self. Who I really am. Not what everyone thinks of me, not what I think I ought to be. But reality.
I heard on NPR last night what had to be done to save the severely burned victims of the 9/11 attacks. The peeling of burned tissue, under anesthesia. The transplants of artificial covering. And at the last, the transplants of the patients' own skin.
We are all like that. We need, after the medicos have done their magic, to be again ourselves.