It just occurred to me that Mephiston's coming out the otherside of the Black rage....he's a master psyker....he came back from certain death....he was swiftly exfiltrated by the Eldar I believe.....
Some similarities with some of the heresy story lines could make a neat revelation.....
Who else in the 40k universe might be one of the perpetuals? Saint Celestine is it? The grey knight justicar dude? The Black Templar chaplin Grimaldus?
Any others?