I.M. Foreman was a Gallifreyan monk who lived on Gallifrey but was driven from the monastries following Rassilon's intuitive revolution.
In the wilderness he found 12 individuals all of whom had no memory of who they were.
They formed I.M. Foreman's One-Species Nongenetically Engineered Travelling Show a show which is 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, much less stable then compared to modern regeneration. Meaning he tended to absorb the DNA of whatever he encountered.
I.M. Foreman eventually arrived on Dust where his true nature was revealed to the Third Doctor and Sarah Jane Smith.
I.M. Foreman's travelling show is made up of thirteen acts, which are all aspects / bodies of I.M. Foreman, one for each regeneration.
When The Remote attack the planet they let out Number 13, the most unstable of all his regenerations which tries to eat everything and absorb it into its own structure.
Eventually it blends itself with Magdalena and the planet [[Dust (planet) | Dust).
The other regeneration aspects are sent back through time, their travelling show exploding as it ends up back in the Dark Times just before the first I.M. Foreman finds then triggering a regeneration for all 12 aspects.