The First

The First was the very first sentient lifeform in the universe. She saw herself as the mother of all living things. She slept for billions of years, waking to find her children fighting, causing wars and sadness. This caused her to create a Reality Virus, to wipe out all creation and start again.

The Thirteenth Doctor and the Player stopped her by sealing her in a timeloop. (NOTVALID: The Edge of Time)