Sounds like the Adeptus Custodes to me. If you are wanting something similar to them, look up articles of them. A GW employee made a big army of them in WD sometime back as well. If the Emperor himself chose them, some 10k years ago, they would be brilliant tacticians, have an aptitude for war and charisma, and be utterly loyal to the Imperium. It is stated, especially in the new books, that he didn't care much for thinking of himself or others doing so, so the chamber militant would most likely be there specifically to protect something he would have considered vital back then. They would seem more likely to be Tau-ish in doctrine, seeking to unite all humans under the Imperium banner. I see alot of oratory abilities and tactical brilliance.
Since back then there were so many different human variants, I wouldn't doubt if some used alien or near-alien weaponry. It would have to be the successor or progenitor of the Custodes.