I.M. Foreman was a Gallifreyan monk who lived on Gallifrey but was driven from the monasteries following Rassilon's Intuitive Revolution.
In the wilderness, he found 12 individuals all of whom had no memory of who they were. Together 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 less stable than compared to modern regeneration,meaning he tended to absorb the DNA of whatever he encountered.
He eventually arrived on Dust where his true nature was revealed to the the Doctor and Sarah Jane Smith. I.M. Foreman's travelling show was made up of thirteen acts, which are all aspects / bodies of I.M. Foreman, one for each regeneration. When The Remote attacked 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 blended itself with Magdalena and the 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 twelve aspects.
From at least the early 1960s to at least the mid-1980s, there was an I.M. Foreman junkyard located at 76 Totter's Lane in London. It was here that the Doctor parked his TARDIS for several months in 1963 as he worked on securing the Hand of Omega (DW: Remembrance of the Daleks); his grandaughter adopted the name Susan Foreman from the location (DW: An Unearthly Child). The connection between the junkyard and the Time Lord I.M. Foreman, if any connection exists, remains unclear.