The grey man's race
The Grey Man was one of an ancient race who influenced the structure of the universe, (PROSE: Falls the Shadow [+]Loading...["Falls the Shadow (novel)"]) 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)"])
The race already existed before the origins of life; (PROSE: Falls the Shadow [+]Loading...["Falls the Shadow (novel)"]) by one 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)"])
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)"], they are not brought up in Falls the Shadow [+]Loading...["Falls the Shadow (novel)"].
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 which strongly recalls Falls the Shadow's account of the "first species", 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.
However, within Falls the Shadow, the Seventh Doctor seemed to be certain that the Grey Man "was not a Time Lord", and the Grey Man seems to refer to them as separate from himself.
