The Grace are a benevolent group of Great Old Ones whom created the Key to Time. The Black and White Guardians were their agents. They existed outside of time and space, in a state of non-existence. It was a group which worked at keeping the universe together, and when necessary entered reality to prevent its collapse. Beings which were too big to enter normal time and space. The Doctor imaged hem as "big, peaceful, pan-dimensional creatures with enormous power". Entities whom for brief periods could stop time and with a thought could crush the Doctor.