The Emperor

The Emperor was the supreme ruler of the universe in the far future, as well as the biological father of Miranda Dawkins.

The Emperor was a Time Lord, the last survivor of a great catastrophe that completely ravaged Gallifrey. For a thousand years, the Emperor reigned over the entire universe. (PROSE: Father Time)

He controlled time and space travel with a ruthless secret police force. He crushed any rebellion before it even began. The Emperor controlled the Senate of his empire through fear. He ruled from his throne on the Needle. (PROSE: Father Time) He was seen in a vision by the Eighth Doctor and Marnal as one of the last surviving Time Lords after the destruction of Gallifrey. In the vision, the Emperor held his newborn daughter in his arms on the night he was killed. (PROSE: The Gallifrey Chronicles)

On the night of his daughter's birth, the Emperor was assassinated by rebels. The entire empire fell into chaos overnight because the child was hidden away on Earth in the 1980s. (COMIC: Miranda)

Behind the Scenes
The Emperor was hinted to be a future version of the Doctor, though this was never confirmed in-text. (PROSE: The Gallifrey Chronicles)