Mole Mann

“There was a place in Hell where skulls were the only ornaments, and the servants had no faces. Even from there he had been cast out. As a shadow of a shade he came to dwell at the edge of a certain abyss, in a tower built out of the bodies of those he had personally marked when he had been allowed in the dark councils of Mictlan. This happened soon after the masters of the Celestial Intervention Agency, the Celestis, had pulled the doors of perception closed behind themselves lest their histories be unravelled in the war with the Time Lords’ future enemy, in the battles they had foreseen. They had put reality behind them like a bad dream and turned themselves into creatures built out of mythemes and the working of nanoscopic machine-demons. They had poisoned the walls of reality itself, until Mictlan had bubbled up into existence on its far side, a cyst of galled space-time cut off from the time winds. It was their glorious world of the dead.”
― Simon Bucher-Jones, Doctor Who: The Taking of Planet 5