The Gestalt

The Gestalt was a mysterious, immortal psychic entity made up of a great number of different minds, who did not always agree with one another. Although occasionally secretive, the Gestalt were benevolent, directing their chosen hosts to righting various wrongs across the universe.

Nature
The Gestalt needed to possess a physical being to influence the universe, and would die if their current host died without passing on the Gestalt. To do so, there needed to be mutual agreement between the current host and prospective successor, although this could come in the form of the successor agreeing to carry on the predecessor's work without truly understanding the implications of their pledge. Once they possessed a host, the Gestalt would speak to them in their mind but also alter their biology, giving them increased durability and augmenting their lifespan, keeping the host constantly "rejuvenated" — which even obviated the need for sleep in an emergency, although hosts could still sleep if they chose. The Gestalt's host would have access to the Gestalt's timeship. (PROSE: Ring Theory)

Origins
Kady Williams believed that the Gestalt had once been a physical being before arriving at their current state of existence. She sometimes had dreams about a veiled priestess, who she occasionally speculated might be the Gestalt's original identity, although at other times she thought the priestess might simply have been an early host. (PROSE: Ring Theory)

Hosts
At one point, long before they possessed Kady, the Gestalt were (as they admitted to Kady) "not as nice" as they would later become. They possessed a Gendar known as Filin. Filin was offered a deal by the Superiors, to help them convert an aberrant Cwej into a more stable memetic entity in exchange for their nudging the timeline of the planet Gendar away from the mortal danger which it was currently facing. The minds within the Gestalt were split on whether to accept the offer, and Filin eventually agreed, to the Gendar's later regret.

The Gestalt's later hosts included a woman who, as she was dying, passed the Gestalt onto a human known as Kady Williams, who didn't truly realise what she was agreeing to at the time. Nevertheless, Kady adapted well to life as the host of the Gestalt, acting as such for several years and only once attempting to disobey their directives, when they asked that she sacrifice her stepson Bill for the greater good. At one point, Kady briefly agreed to transfer the Gestalt to the memetic entity created by Filin, the Gentleman, who was now threatening Kady's life as well as Chris Cwej's, Larles's and Kwol's. However, this was actually a ploy to defeat the Gentleman: as a memetic entity, the Gentleman soon found his will overridden by the many combined wills of the minds within the Gestalt, who were able to make use of the Gentleman's own powers to create an exit from the labyrinthine crashed space-ship where the Gentleman was keeping Kady, Cwej, Larles and Kwol trapped. The Gentleman was then finished off for good, and as he died, the Gestalt transferred themselves back into Kady. (PROSE: Ring Theory)

Behind the scenes
The Gestalt's timeship is described as having a blue, rectangular exterior, suggesting the Gestalt may potentially be a future form of the Doctor. One of the voices within the Gestalt in Ring Theory has a Scottish accent and, at the end of the story, has the line "It’s time to leave, Kady. We’ve got work to do". This resembles the Scottish-accented Seventh Doctor's final line in the classic series at the end of Survival ("Come on, Ace, we've got work to do!"), furthering the suggestion that the many voices within the Gestalt may be past incarnations of the Doctor.