Council of Eight

The Council of Eight were an organisation created to fill the gap when the Time Lords were wiped out.

Biology
The Council of Eight physically resembled eight crystalline entities that bore similarities to the first eight incarnations of the Doctor. (EDA: Sometime Never...)

Technology
The Council had the technology to engineer deaths for people. Their victims included Sarah Jane Smith, Ace and Samantha Jones. Their Time Station, anchored in the Time Vortex, had a treasure trove of technology in the Schrodinger Cells, specialised facilities for holding prisoners that removed them from time and drew tremendous amounts of energy out of the unfulfilled potential futures of the people within. This, however, had a key flaw: opening a Schrodinger Cell had dire consequences; all potential futures collapsed as the prisoner shifted back to normal time, therefore shutting off the energy siphoned off by the Cell. (EDA: Sometime Never...)

History
After the destruction of Gallifrey, the Council of Eight created their fortress in the heart of the Time Vortex so that they could become the new Lords of Time. As the Council gained power by successfully prophesying future events, they were naturally inclined to remove all free will in the universe and create one where all actions could be accurately predicted by the Council, therefore making them invincible. To this end, they convinced Sabbath that parallel timelines were causing damage to the "prime" reality and that by destroying them he would be able to steer humanity to the path of the masters of the Universe. (EDA: Sometime Never...)

The Council went to war with the Clock People for control of the time vortex. They manipulated the Eighth Doctor into destroying their opponents, leaving them in complete control of the vortex. (EDA: Anachrophobia)

They considered the Doctor to be an unpredictable factor and thus feared and wished for his destruction. To weaken him, they began taking some of his old companions out of history and locking them into Schrodinger Cells in their Time Station or outright killing them.

Leading the Doctor to a trap in the Time Station, they began preparing a massive ontological paradox, intending for Sabbath to kill Octan, the leader of the Council, so the rest could ascend to omnipotence. However, the Doctor discovered their plans and tricked Octan into revealing his plans and their manipulation of Sabbath. Sabbath, realising his horrific mistake, shot himself rather than fulfil the destiny laid by the Council, thwarting their plans, but not before Miranda Dawkins, the Doctor's adopted daughter, had died in the Station.

Furious and terrified that the chain of causality they had engineered had failed, they tried to kill the Doctor, only to fail when Octan, mad with horror and confusion, began opening the eight Schrodinger Cells fueling their Station; upon being tricked by the Doctor, history began to change so as each Cell opened, the remaining ones were increasingly likely to be empty, therefore shutting down the Station. Desperate for a solution, Soul, the youngest of the Council, opened Schrodinger Cell Eight, releasing the possibility of parallel universes so the Council had a possibility to survive in an alternate world.

Soul escaped in the Jonah, Sabbath's timetravelling vessel, with Zezanne, Miranda's daughter, in hopes of finding a better world to live in. He adopted the shape of an old man, and as they escaped, the hourglasses used to keep their time in the Station were damaged, resulting in Soul believing he was the Doctor, with Zezanne thus regarding her as her grandfather. The Jonah then materialised in a London junkyard, assuming the shape of a Metropolitan police box... (EDA: Sometime Never...)

Behind the scenes

 * Sabbath's allies were (supposedly) meant to be the Daleks, but copyright problems prevented this.