Higher Evolutionary

Higher Evolutionaries or High Evolutionaries were the oldest and most powerful time-aware beings in the Universe and included Time Lords, Lords of Althrace, Merlin the Wise, (DWM: The Tides of Time) members of the Order of the Black Sun, and many more across at least a billion planets. (DWM: The Final Chapter)

When Melanicus took control of the Event Synthesizer, representatives began to gather from the furthest reaches of the cosmos. Although Rassilon believed that the Time Lords alone could handle the situation, his two fellow Matrix Lords pressured him to recognise the other Higher Evolutionaries. Within the Matrix, a six member council was formed which included members more familiar with the history of Melanicus and the Event Synthesizer.

The Doctor met with this council and was tasked with restoring the Event Synthesizer. From the Althrace system, he witnessed the creation of a universe-wide network of the minds of High Evolutionaries using Shayde's connection to the Matrix to complete the circuit. Their combined mental faculties were able to transcend concepts of space and time to locate the still moment where the Event Synthesizer was. (DWM: The Tides of Time)

The Evolutionaries would hire the Threshold to try and prevent the Daleks from invading parallel universes. (DWM: Fire and Brimstone, Wormwood)

The Doctor's mind would be summoned to them when he was hospitalised on Gallifrey. They warned him of a vision they all shared of Gallifrey turned into a violent empire even though the Elysians had not yet made their attempt to form this alternate timeline. By this point, Merlin had been replaced by Demoiselle Drin. (DWM: The Final Chapter)

Rassilon's council

 * Rassilon
 * Merlin the Wise
 * Dakon Theka
 * Thane of Kordor
 * Morvane
 * Bedevere
 * Demoiselle Drin (replacing Merlin)

Behind the scenes
The Marvel Comics title Captain Britain And MI:13 written by Paul Cornell mentioned in #2 that "the Higher Evolutionaries of all the worlds" have imprisoned Merlin in a realm of dark magic. Merlin here was shown to be the Doctor Who Magazine Merlin, already established by Alan Moore in The Daredevils to be a guise of their Merlin.