as a long time diablo player - well, since the game got out - i consider this part of lore questionable and probably of a later date. The Wanderer, the d1 protagonist, acts and talks like he has absolutely no connection to either tristram or royal line - furthermore, his knowledge of leoric, lazarus and the diablo "situation" originates from deckard cain, and not from his own recent past. furthermore, he isn't recognized by either resurrected leoric, lazarus or any of late king servants, which is rather improbable for a heir to the throne - not to mention that one of the classes is female-only (though game animation always portrait protagonist as male), and therefore unsuitable to both name "Aidan" or fathership of Leah.
The Wanderer of original diablo is a "accidental hero", a tragic figure who sacrifices himself in uncertain attempt to prolong diablo return - contradicting the statement that "diablo saw suitable vessel in him" - he considers himself a rather unsuitable, similar to tal-rasha.
in a same manner, "Aidan" proposed fatherhood to Leah seem directly opposed to his character - a character who willingly sacrifices himself for common good is not likely to risk having a child while carrying a soulstone in his head. furthermore, protagonist leaves tristram and heads east immediately after diablo is defeated, in search for cure/salvation.
in my opinion, whole Aidan/Adria/Leah part of lore is inherently flawed Clavdivs, The God
- The lore went through a retcon as Blizzard was working on Diablo III. Sojourna 01:50, 22 August 2012 (UTC)
It does seem odd about the Wanderer being Aidan, it provides many plot holes and a lot have been retconned but like the manual was made into flavour lore, but that still makes it weird that no one would have known who he was so maybe he was a bastard child but that still doesn't explain why Cain or Marius wouldn't have called him by his name, it is stated in the Book of Cain that Cain couldn't call him by his name but then why didn't Marius either!? Also why would he have had a baby with the witch especially if he was fighting for his sanity and holding off Diablo. Also Ogden's dialogue says that he knows you when you enter the town so that also is quite odd.