The Celation Nebula, referred to simply as Celation, with one manifestation known as the Master of Celation, was a sentient nebula (AUDIO: The Perfect Prisoners) and a delegate of the Galactic Council who allied with the Daleks in 4000.
The sentient Celation Nebula drifted through the spiral arms of the Mutter's Spiral. Its particles were capable of splitting apart and coalescing, letting its pieces take forms of their own, including humanoid form. Typically, Celation took humanoid form only as a courtesy, for the purposes of amiable communication with other lifeforms. As such, they were beyond concepts like gender, being indecisive and frequently changing the form they took. (AUDIO: The Perfect Prisoners) In 4000, Celation took the form of a bald male humanoid with black spots. (TV: The Daleks' Master Plan) Another of their forms, later in the 41st century, was a female humanoid. (AUDIO: The Perfect Prisoners)
Celation had apparently been persuaded to join the Daleks' alliance by Zephon. When Zephon attempted to leave the alliance, he expected wrongly that Celation and Beaus would join him. Along with Trantis and Mavic Chen, he was one of the most powerful leaders of the alliance.
The execution of Trantis ensured Celation's loyalty to the Daleks, but his jealousy and rivalry with Chen led to the end of the alliance. He became the most forceful opponent of Chen, demanding his expulsion from the Council, but after they were betrayed by the Daleks, he planned with Chen, Beaus, and Malpha to form a new Galactic Council. He agreed to return to his own people and warn them about the Daleks' invasion plans and help fight them, if Steven Taylor and Sara Kingdom would free them. (TV: The Daleks' Master Plan)
The Master of Celation later informed Zephon's family of his betrayal by the First Doctor, who framed Zephon as a traitor. The Lady Zephon had to convince Vice President Zephon that Zephon was not a traitor, and this information later prompted Zephon's son, Zephon to join the Syndicate. (AUDIO: Time's Assassin)
As part of the Syndicate, Celation and survivors or relatives of the Galactic Council attempted to rule the galaxy, but the Fourth Doctor began tracking them in an attempt to stop them, not knowing that his companion, sleeper time agent "Ann Kelso," was killing the Syndicate members as they found them. Fearful that the Doctor would come for them all, Celation and Malpha backed out of the Syndicate when Trantis III and Sentreal where killed. Celation took it upon herself to kill the Doctor, with the nebula forming around the spaceship he was on, planning to condense the ship into a singularity. However, in her mission to kill the Syndicate, Kelso overloaded the ship's reactor, and although the Doctor tried to warn Celation, he was too late; as they escaped onboard his TARDIS, the explosion irradiated the Nebula, seeminly killing Celation. The Doctor found no life signs on his return. (AUDIO: The Perfect Prisoners)