Number Thirteen

I.M. Foreman was a Gallifreyan monk who lived on Gallifrey but was driven from the monasteries following Rassilon's Intuitive Revelation. He was not a Time Lord, but was able to regenerate due to his order having received its own version of the Rassilon Imprimatur.

Biography
Having been exiled to the wilderness after the dissolution of the old religious orders, I.M. Foreman found twelve individuals, all of whom had no memory of who they were, but who they eventually deduced were his future twelve incarnations. Together they formed I.M. Foreman's One-Species Nongenetically Engineered Travelling Show, a show which was actually a complex space time event that could travel in time. As a priest, he had been given the gift of regeneration, but in those days it was much less stable than modern regeneration, meaning he tended to absorb the DNA of whatever he encountered in his life whenever he regenerated, each of his incarnations being increasingly less human as they moved on from his original body.

He eventually arrived on Dust, where his true nature was revealed to the Third Doctor and Sarah Jane Smith (after the TARDIS was unintentionally diverted to Dust after an accidental meeting between the Third and Eighth Doctors). I.M. Foreman's travelling show was made up of thirteen acts, which were all aspects/bodies of I.M. Foreman, one for each regeneration. When the Remote attacked the planet, the other twelve were forced to release Number 13, the most unstable of all his regenerations, which tried to eat everything and absorb it into its own structure.

In order to conclude the time loop and prevent the death of the past twelve Foremans causing a paradox, the other regeneration aspects were sent back through time thanks to the Doctor linking the show to the TARDIS and sending it back to Gallifrey's distant past. Arriving at its destination with no arrival site prepared for it, their travelling show exploding as it ended up back in the Dark Times just before the first I.M. Foreman found the show. The resulting explosion and the fall from the ship triggered a regeneration for all twelve aspects, each of them changing into their next self while losing their memories due to the trauma of the damage and the limitations of their current ability to regenerate.

Back in the present, after Number 13 consumed the attacking Faction Paradox fleet, the Doctor was able to convince it to blend with the planet Dust to turn it into a new, vital world. With the crisis concluded as the planet grew more vibrant, Foreman's consciousness formed a bond with Magdelana Bishop and inhabited her body with her consent. In this form, Foreman spent two days in the company of the Eighth Doctor, during which she talked with him and spent the night with him. (PROSE: Interference - Book Two)

76 Totter's Lane
Foreman's show spent some time at 76 Totter's Lane, which later was the junkyard where the First Doctor first met Barbara Wright and Ian Chesterton. Susan Foreman, the Doctor's granddaughter, may have adopted her surname from the lettering on the gates; when the Third Doctor learned of Foreman's existence, he realized that the TARDIS had been drawn to the scrapyard because it had been aware of the show's previous presence there.

Incarnations
I.M. Foreman's thirteen incarnations were as follows:
 * I.M. Foreman was the original incarnation, he put out his own eyes to increase his natural telepathy, and used stigmata as his "act" in the show to represent the blood that carried the genetic potential.
 * Mohandas, the Geek was mostly humanoid, but gave off a strong scent of the animal matter he has consumed; has made it his life's mission to consume everything he can.
 * Melmoth, the Map of Scars was a human figure covered in scars that represented the various genetic codes of the creatures that he had consumed in his previous life.
 * Mr Zarathustra, the Walking Brain: A humanoid with an enlarged head, capable of communicating only via telepathy.
 * O'Salamander, the Dragon-King was half-man, half-lizard, but so constantly in flux that observers could not subsequently recall which side was which.
 * John Salt, the Missing Link was a humanoid covered in albino monkey fur.
 * Mould, the Worm-Boy was a man who crawled along the ground on his belly like a maggot; noted as having a habit of leaving goo on Foreman's boots.
 * The Goofus, the Living Armoury: The only incarnation to incorporate machinery.
 * Ezekiel, Master Aerialist was the only incarnation to develop wings, but the results were less than promising; observers noted that Ezekiel would only be capable of gliding at best.
 * Queen Nitocris, Mistress of Serpents was a very serpent-like female incarnation.
 * The If represented the Time Lords' links to their time machines, it possessed raw time-travel biodata that allowed it to perceive the past and future of anyone it met.
 * AKA, the Metamorph was a representation of all the DNA that Foreman had absorbed over the course of his lives, constantly shifting forms from one moment to the next, resulting in AKA representing a blur more than a single lifeform.
 * Number Thirteen was a raw force of nature and the essence of everything the previous twelve had consumed. Number Thirteen existed to consume as much life as possible, and was kept contained for centuries until the final "act" on Dust.