Public Info: Xellos appears to be an ally of Amestris, and has a good deal of magical skill and quite the silver tongue. Calls himself a priest, and seems to know a number of secrets.
Snoopers Info: Seems to travel great distances much quicker than a normal person should. Careful observers will notice a tendency to stick to the edges of battle, and he rarely ever takes part in it himself. Seems to avoid perky/upbeat/positive individuals.
Title: The Mysterious Priest - he'll probably get labeled as a coward and the like the more he's active.
What must not be known: That he's actually a Rift creature. Currently only Caster knows this - Roy may learn it soon. Shiki Eiki knows that he at least isn't human. I don't mind people being suspicious about what Xellos actually is - he's got some obvious tics that put him as not being normal, but I'd generally like to be checked with prior to someone figuring him out.