The Grey Man was one of an ancient race who sometimes "styled themselves" as gods. They influenced and solidified the structure of the universe, whom he called "[his] people" or "[his] colleagues" (PROSE: Falls the Shadow [+]Loading...["Falls the Shadow (novel)"]) and who were referred to in one history book as the grey man's race. (PROSE: A History of the Universe [+]Loading...["A History of the Universe (short story)"]) Although the Grey Man manifested in a human-like body, which he could replace if it was destroyed, he referred to a separate species who had appeared after his own kind as the first humanoids. (PROSE: Falls the Shadow [+]Loading...["Falls the Shadow (novel)"]) By some accounts, the oldest race in the universe who hardened the structure of reality were the Time Lords of the Great Houses, (PROSE: Crimes Against History [+]Loading...["Crimes Against History (short story)"], TV: The Sound of Drums [+]Loading...["The Sound of Drums (TV story)"]) although when he initially met the Grey Man the Seventh Doctor felt "certain" that he was not a Time Lord.
By the Grey Man's telling, his race existed before the origins of life; (PROSE: Falls the Shadow [+]Loading...["Falls the Shadow (novel)"]) by the history book's account, it had been formed alongside other forces such as the Guardians in Event One, (PROSE: A History of the Universe [+]Loading...["A History of the Universe (short story)"]) although the Grey Man's own account did not clarify whence his race had come from, nor whether it preexisted Event One, and made no mention of the Guardians. The Grey Man related:
Fifteen thousand million years ago, the cosmos formed during Event One. There was a hydrogen rush which defined the parameters of the mate- rial universe. The implications and resonances of Event One go beyond that simple explosion, but they don’t concern us… Suns formed. Systems formed. Life blossomed on a million planets. And when the first cells spawned in the first oceans on the first world, I was there, with my people, watching.
After the aforementioned first mundane humanoid species evolved, the Grey Man and his "colleagues" watched them for "ten thousand years", growing emotionally invested in their turmoils. One day, however, war broke out within the species and they destroyed themselves. The Grey Man saw, in their senseless a violence, a "madness" external to the mortals' own way of thinking, and realised that his colleagues were responsible for the introduction of "them and us", "good and evil" and all other such absolute dualities to their noosphere:
There was a madness manifest in the design of that virus. (…) Polarisation and duality. Undiluted absolutes. Fine for chess but chess is a game, and these concepts had been applied to the real world. I call it madness. It was nothing of the kind. (…) There were other agencies at work. Not alien forces, because no such things yet existed. I investigated and I found… found the influence of my people, of my race. They had developed the madness because it suited their own purpose, it suited the rivalries and the tensions that divided them and to which I had not been a party. Their influence stretched through the cosmos, down to the universal structure itself. There is a structure – perhaps, it is difficult to explain – but it is a loose and pliable one. They had taken it and were making it rigid, imposing their own philosophies, their absolutes. They had taken the people of the first world to war. They had destroyed the oldest civilisation for their own fathomless motives. I do not understand why. Perhaps they were jealous, perhaps they hate those who live the real life that has been denied to them. Perhaps they wish to be worshipped as if they were gods – they style themselves as such. I have never understood, perhaps I have not tried.
He fled "[their] home" and created Cathedral in an effort to inject ambiguity and free will into the universe. He hid it in a pocket reality, making sure his people would not discover it. He himself, however, "long[ed] to see it again" and returned to this "home" where he was "immediately placed on trial by [his] colleagues" for his so-called blasphemy. He was "cast out", "fell", and "burned", essentially dying; his mind only survived as part of Cathedral, though he could project himself from it into the universe, the form in which the Doctor and Bernice Summerfield would eventually meet him when humans studying interstitial time stumbled on the secrets of Cathedral. (PROSE: Falls the Shadow [+]Loading...["Falls the Shadow (novel)"])
Behind the scenes
The Grey Man's race is never given a name, with him referring only to "[his] colleagues" and other such periphrases. One obvious interpretation is that they are the Guardians of Time, as they are stated to be responsible for introducing manichaean duality to the universe; the Grey Man would thus be positioned as a midway point between the Black Guardian and White Guardian, filling a part similar to the balance-bringing Red Guardian in Craig Hinton's unrelated effort to expand the Guardians' ranks. Although the "grey man's race" and Guardians are discussed separately in A History of the Universe [+]Loading...["A History of the Universe (short story)"], the latter are not brought up in Falls the Shadow [+]Loading...["Falls the Shadow (novel)"]. HoFurthermorewever, the Grey Man is shown to have the same abilities of control over the Doctor's TARDIS that the White Guardian does in TV: Enlightenment [+]Loading...["Enlightenment (TV story)"].
As the first sapient race, who used their position to impose a metaphysical "structure" on reality in the early universe, they also strongly recall the Time Lords as they would go on to be reimagined in Faction Paradox (for which Daniel O'Mahony would go on to write), as the archons of the Great Houses. Crimes Against History [+]Loading...["Crimes Against History (short story)"], for example, opens on an explanation of the archons' origins which strongly recalls Falls the Shadow's account of the grey man's race, and brings caveats to their description as humanoid or a species at all, thus explaining their distinction from the first humanoids in Falls the Shadow.
The first sentient life in the universe develops. The culture in question can reasonably be described as humanoid, and immediately begins to imprint its own ideas about how things should work on the universe around it, hence the proliferation of humanoid forms throughout the rest of history. As the first self-aware tenants of creation, this primal culture can't strictly be considered "alien", or even a species, as such: these are the ones who set the template for the rest of sentient life, and therefore can only be considered a force of nature, or at the very least a force of history.
The discussion of the Grey Man longing to return "home", and being placed on trial when he did, is evocative of the Doctor's own status relative to the Time Lords, particularly in the William Hartnell and Patrick Troughton eras.
However, within Falls the Shadow, the Seventh Doctor's first impression of the Grey Man includes the detail that he is "certain that whatever the grey man might he, he was not a Time Lord"; furthermore, the Grey Man seems to refer to them as separate from himself, once noting: "I have no affection for the Time Lords of Gallifrey, nor any mayfly-race that claims for itself the status of gods". However, a measure of ambiguity is added by another passage of Falls the Shadow where the Doctor himself, within his inner monologue, denies being a Time Lord ("…i am what i am i am not a time lord i reject the title i am myself i am a doctor and healer a good man…"); one of the Grey Man's statements about his own race is a similarly-dismissive judgement of them for "styling themselves" as gods.
Yet another and even more straightforward guess, not necessarily incompatible with a conflation with the Time Lords, would be that the Grey Man's "people" are abrahamic angels. The Grey Man's reference to having "fallen" and "burned" after he was placed on trial for "blasphemy" by his people evokes the classic imagery of fallen angels. This would seem to place the internal "rivalries" among his people which translated into the introduction of Good and Evil to mortal experience as the biblical War in Heaven sparked by the Devil's rebellion.