Prime Dalek (The Thousand Worlds)

A Prime Dalek led the Daleks on the planet Keska.

Biography
During the Last Great Time War, the War Doctor was sent on a quest by Cardinal Ollistra to investigate the Daleks' plan on Keska. After reuniting with Rejoice, she informed the Doctor that the Daleks and the Taalyens were led by a Prime Dalek. The Prime Dalek announced that the drilling machines would drill into the planet's core and destroy the core, a plan the Doctor had seen before. Seratrix insisted that he was working for the greater good and that their plan would lead to a peace with the Daleks, who would rule the Null Zone. Later, Seratrix revealed that the Time Lords gave the Daleks the weapon that created the Null Zone, in response to the Doctor’s use of the Time Destructor to destroy the Dalek time fleet. He explained that the plan of the Daleks was to put hyperdrives in all the thousand worlds and move them to create a defended border around the null zone. (AUDIO: The Thousand Worlds)

The Doctor countered that the Daleks don’t do defensive; they only attack because they irreversibly believe all life to be inferior to them and he suggested he could prove the Daleks were up to something worse. As soon as they got to the Control Room, the Doctor put his plan into action. Calling himself "John Smith" to avoid the Daleks from recognising him, he feigned to help the Prime Dalek restore his communications with the drill. The Doctor pulled up a schematic which showed that the real plan was to launch the thousand worlds at fifty times the speed of light at Gallifrey, utterly destroying it. Seratrix still tried despairingly to plead for peace but was exterminated by the Daleks. Before they could fire on the others, Veklin set off the charges, which destroyed the pathweb that let the Daleks communicate; the relevant overload deafened and overwhelmed the Daleks, knocking them out. (AUDIO: The Heart of the Battle)