The Imperator

 was a notorious and malevolent member of House Dvora. He was one of a generation of rebels caused by the introduction of foreign biodata to the breeding engines.

He rose to power over the High Council of the Homeworld and demanded that the Protocols of the Great Houses be forgotten and history itself be redrawn to better suit Gallifrey's needs. After he was denounced by the Order of the Weal, he and his followers (recruited from the lesser species) wreaked havoc throughout history until he was executed by the Great Houses.

His presidency shook Time Lord society to its core, led to the formation of groups like the Celestis and Faction Paradox, and set precedent for the creation of unimaginably violent and dangerous weapons and warfare for the War. (PROSE: The Book of the War)

Behind the scenes
The Imperator is the name used for Morbius in the Faction Paradox series.