Alternate timeline (Time & Time Again)
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 Earth in 1993.
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, Neomorph Cybermen, Ice Warriors, Draconians, Sea Devils, early Silurians, Terileptils, and Zygons.
When the Seventh Doctor arrived within the chaos he was instructed by the White Guardian to retrieve the Key to Time, which would allow him to restore the correct frame of reference for the universe.
The Doctor, Ace and Bernice retrieved the segments which had been scattered along the Doctor's time track, allowing the White Guardian to restore the universe. Back on Gallifrey, the First Doctor and Susan decided to steal a TARDIS and leave to protect the Hand of Omega. (COMIC: Time & Time Again)
