Zagreus

 was the name given to an anti-time creature that was formed after a mass of anti-time entered the Doctor and became sentient. The name "Zagreus" was taken from a legend created by the Neverpeople.

History
Legends stated that Rassilon himself destroyed Zagreus when the Yssgaroth came into the universe in the events around the creation of the Eye of Harmony. It was said by the Neverpeople that when a casket of anti-time was detonated at the Capitol, chaos would engulf the Universe and the empire of Zagreus would form. When the Eighth Doctor prevented this event by materialising his TARDIS round the casket, he absorbed the anti-time particles into his own body. He became a dark being and the embodiment of Zagreus. (AUDIO: Neverland)

Life inhabiting the Doctor
The Doctor's true personality remained intact, though submerged by Zagreus's strength. The TARDIS was fractured in a similar way, torn between its attempt to help the Doctor and its resentment at his willingness to sacrifice it for Charley. While the Doctor tried to regain control of himself, the Zagreus-TARDIS projected an interface based on the Brigadier, and sided with Rassilon to turn the Doctor fully into Zagreus, who would serve as Rassilon's assassin, in exchange for Rassilon freeing the TARDIS from the Doctor's "enslavement". This would be achieved by pretending to destroy the TARDIS's shell to sufficiently traumatise the Doctor into allowing Zagreus full control of his body. However, the TARDIS's true nature retained enough control as to generate holograms of Reverend Matthew Townsend, Lord Tepesh and Walton Winkle (whose appearances were based respectively on the Doctor's fifth, sixth and seventh incarnations), who helped the Doctor remember who he really was, whilst also aiding Charley with the fragments of the Doctor's knowledge they still possessed, despite their new backgrounds.

Despite Rassilon's efforts to reaffirm the Doctor's status as Zagreus, both personalities rebelled against Rassilon's plans, with the Doctor refusing to kill while Zagreus refused to be anyone's puppet. With the Zagreus-TARDIS having been destroyed by Charley, Leela and Romana II when it was knocked into the vat the TARDIS was being melted down in, the Doctor and Zagreus together banished Rassilon into the Divergent Universe before the TARDIS, partially restored due to the Zagreus-TARDIS being mixed with its remains, was able to provide his companions with a cure to the anti-time energies in the form of pure zero matter, simultaneously restoring the TARDIS to its normal police box form. However, although the zero matter stabilised the Zagreus "infection" within the Doctor so that the Zagreus personality would now be dormant while the Doctor regained full control of himself, the Doctor had to remain in the Divergent Universe, a universe without time, to prevent the anti-time still within him from destroying his own universe. (AUDIO: Zagreus)

Life as Perfection
The anti-time energies were purged from the Doctor by Rassilon when he entered the Divergent Universe. This let Zagreus manifest as an independent entity. In this form, Zagreus could possess the bodies of the dead, and confronted the Doctor in the body of Perfection, the "perfect woman" and wife of the most powerful man in the Divergent Universe, Daqar Keep. She tried to trick the Doctor into taking her into the main universe by working with him in the hunt for the Foundry. During this time it enjoyed a flirtatious relationship with the Doctor, even proposing at one point to repopulate the Divergent Universe with their children (as the universe was seemingly facing extinction), her "Eve" to his "Adam". When she used this legend, which only someone from the Doctor's universe could know, the Doctor saw through her deception, but she had already incapacitated Keep and hypnotised Charley by the time he took action. She attempted to escape into the Doctor's universe in the TARDIS, but in reality she just entered the shape-shifting Keep who had adopted the appearance of the ship, causing her to become trapped in his body long enough for the Doctor and his companions to leave in the true TARDIS. Now stuck in the Divergent Universe with no hope of escape, Zagreus accepted Keep's proposal that, rather than fight, they should renew their wedding vows and seize control of the Divergent Universe. They both stated that it would be very "diverting". (AUDIO: The Next Life)

Zagreus rhyme

 * Zagreus sits inside your head,
 * Zagreus lives among the dead,
 * Zagreus sees you in your bed,
 * And eats you when you're sleeping.


 * Zagreus at the end of days,
 * Zagreus lies all other ways,
 * Zagreus comes when time's a maze,
 * And all of history is weeping.


 * Zagreus taking time apart,
 * Zagreus fears the hero heart,
 * Zagreus seeks the final part,
 * The reward that he is reaping.


 * Zagreus sings when all is lost,
 * Zagreus takes all those he's crossed,
 * Zagreus wins and all it cost,
 * The hero's hearts he's keeping.


 * Zagreus seeks the hero's ship,
 * Zagreus needs the web to rip,
 * Zagreus sucks time at a drip,
 * And life aside, he's sweeping.


 * Zagreus waits at the end of the world,
 * For Zagreus is the end of the world.


 * His time is the end of time,
 * And his moment time's undoing.

Personality
When the anti-time energies that formed Zagreus left the Doctor, they presumably retained their sentience by taking with them the dark aspects of the Doctor's mind that they had helped to create. Despite this, when Zagreus possessed Perfection's corpse, it had a very different personality than to when it inhabited the Doctor. In contrast to the ranting and vengeful being it had originally been, in Perfection it was calmer, petulant sometimes and openly flirted with the Doctor; it only showed evidence of what it used to be when it was imprisoned by Daqar Keep. (AUDIO: The Next Life)

Behind the scenes
During part three of Zagreus, a couple of alternate/additional lines are recited by the Eighth Doctor and Rassilon:


 * Zagreus sets the skies ablaze.
 * The stars his flame a gleaming...


 * Zagreus is my secret name,
 * Zagreus is the one to blame,
 * Zagreus is the Time Lords' shame,
 * The beast that I've been keeping.