Source: All-Star Superman #2, 6 (2006-7)
Type: Alternate FutureIn the twisty time tale that is All-Star Superman #6, a young Smallville-bound Superman meets three Supermen from the future, all members of the Superman Squad. Though there to capture a Chronovore, one of their number also has a hidden agenda. The Unknown Superman is actually the modern day (All-Star) Superman hiding his identity from his younger self in order to spend a few moments more with Pa Kent around the time of his death from a heart attack.
OR IS HE?!?
The Unknown Superman also appears as a prophetic hologram in issue #2 where he spouts opaque nonsense at Lois Lane. Surely, this isn't the same guy. So my guess is there really IS an Unknown Soldier/Superman hybrid in the year 4500 A.D. and Clark was simply impersonating him. Perhaps he got the idea from the garbled transmission from the future. Maybe there are MANY Unknown Supermen, just like there have been more than one Unknown Soldier. How would we know? They are UNKNOWN.
PROVE ME WRONG.