As part of his revenge for being denied Enlightenment, the Black Guardian created an alternate timeline to kill the Seventh Doctor when he arrived with Ace and Benny on 1993 Earth. In this new timeline, the First Doctor never left Gallifrey and eventually became Lord President, continuously appeasing the massive Dalek Empire. Because of this, and because of its tactical position, Earth had been invaded a dozen times, the attackers including Robot Yeti, Imperial Daleks, Sontarans, Cybermen, Ice Warriors, Draconians, Sea Devils, Silurians, Terileptils, and Zygons.