Triumvirate

The Triumvirate was the name given to a group of three, highest among the Founders of Time Lord civilisation on the planet Gallifrey; (PROSE: Remembrance of the Daleks) more than one account suggested there were as many as six Founders in all. (PROSE: The Infinity Doctors, The Ancestor Cell)

History
The Gallifreyans who would become the Triumvirate overthrew the rule of the Pythia in an event known as the Intuitive Revelation. (PROSE: Cat's Cradle: Time's Crucible)

Omega was a stellar engineer who created a device capable of changing the structure of stars. Called the Hand of Omega, this device was used to "customise" a star called Qqaba, but Omega was lost and presumed dead in the resulting reaction. (PROSE: The Infinity Doctors)

Rassilon was an architect and law-maker who built upon Omega's experiments to provide Gallifrey with the Eye of Harmony, a singularity capable of providing infinite energy. Rassilon was also credited with ending the barbaric period of Gallifreyan history known as the Dark Time. (TV: The Deadly Assassin, The Five Doctors, Remembrance of the Daleks)

The Other was a mysterious figure who ultimately grew tired of wielding absolute power and allowed himself to become part of the genetic cascade which produced new Time Lords in the Looms. (PROSE: Lungbarrow) The Doctor received many of the Other's memories. (PROSE: Remembrance of the Daleks, Cold Fusion, Lungbarrow)