Omegon
The twin brother of Alpharius; collectively, they are the Primarchs of the Alpha Legion. People know less about this guy than they do about Alpharius, so that's pretty much less than jack squat. In fact, people know so little about this guy and his brother that it isn't even known if they are one person or two. This is leveraged by the fact that everyone is either one of these guys or the other, including themselves.
If you don't know anybody who is secretly Alpharius or Omegon, you probably are him (or the other one (or both (or neither))).