Mindcore

The Mindcore was the collection of the Skith race's greatest minds and the sum of all Skith knowledge. A portion of the Mindcore was installed around the fusion core on all Skith starships. It advised and supervised the commanders and their subordinates. The Mindcore appeared as a huge column of light with a series of disembodied heads. (DWM: The First)

Technically the Mindcore was a single entity, with the main concentration kept on the Skith Ownworld and a branch or terminal in each ship connected by a hyperspace link. However, other parts were stationed on the Skith colony worlds. After Ownworld's destruction, one of the colony parts took over as the main part. (DWM: The Age of Ice)

History
The Skith ship Oppressor One landed in Antarctica in 1915, planning to experiment on the fauna there before cataloguing and obliterating the planet. While there they found the Antarctic Expedition of Ernest Shackleton and the Tenth Doctor. The Mindcore declared the mission a failure, since the Doctor's presence indicated the planet had been tampered with. The Doctor infiltrated the Mindcore shortly after, and destroyed the Oppressor One. (DWM: The First)

A mysterious force destroyed the Skith Ownworld and the central element of the Mindcore. One of the subsidiary parts on a Skith colony world sent the Oppressor Two to hunt down Doctor so it could develop time travel to combat the force. The Oppressor Two showed up above Sydney, Australia in 2010 and successfully captured the Doctor and Majenta Pryce, but a conflict between the Skith Leader of Oppressor One and the Skith General of Oppressor Two allowed the Doctor and UNIT to destroy the ship. (DWM: The Age of Ice)