O5-1: "The Founder".
Male. European descent. American origin. Verified post-human lifespan; 148+ years of age. Varying appearance.
A holdover of the occult organizations preceding the Foundation, so he likely benefits from more preservation techniques than merely SCP-006, and he likely possess a large degree of anomalous protection. References have been made to "clad in rags and bones"; obvious occult significance.
One possible identity for the original Administrator.
Evidence strongly suggests that he was born Aaron Siegel in the late 1800s (possibly 1866). Certainly, one Aaron Siegel was a physicist studying at Cornell University in 1891, who disappears from the historical record after this year. This timeline doesn't match what we know of O5-1's activity, but given his position and the reality-restructuring events that have occurred, it's entirely possible.
Rumor has it that he's Gears' father. If true, this would make him the Black Queen's grandfather — my grandfather.
Two contradictory sightings stand out. Once in company of O5-2, appearing as an extremely old man. Once in what appears to be security footage of an underground bunker, appearing as a young teenager.