Okay, I was actually considering introducing the Nameless One's story arc for a Planescape/Forgotten Realms Table-Top game. It's such a good story and my players are unfamiliar with the computer game, that I don't see any problem with actually putting it into the game for an epic storyline.
The issue, of course, is that this isn't a game totally focused around the Nameless One's doppleganger in this world but his storyline will just part and parcel of a much larger and epic tale that everyone will be having bits and pieces thereof.
Some basic logistic difficulties I'm considering.
* No Ressurection: Instead, I'm considering a more story-based version. The Nameless One in this campaign is trapped in a cycle of reincarnation. Aside from the fun Buddhism style allusions that can be drawn from this, it also makes the player characters desire to stay alive longer.
It also makes the practical issues more clear. The player character seizes the body of some poor child every time he's reborn.
* Broadening the Search for the Past: It's one thing in a computer game to have no answers but I was considering the possibilities of what the Nameless One really was in this FR game. What could a being like him do that's so damned awful that the gods themselves won't accept his soul?
* Forgotten Realms Tie-Ins: I'd very much like to tie this story into the rich lore of Forgotten Realms and have his Prime Material homeworld turn out to be intimately linked to his past and origins.
* Fun Ways of introducing it in game: I can't have our characters just running around asking "Where's Pharod?" and "Do you know who I am?" Especially since the quest for identity here will more be a gradual realization he's not who he always thought he was. So I'm open for interesting ways of bringing up the terrible past.
Basically, the horrible realization you're reborn and hounded by souls of the Damned.
I'm not looking to start up some huge discussion here, but just a sidenote--having immortal player characters can, when done with the right group, be downright fascinating. Most table-top games automatically start with the assumption that survival is your key motivation; when you take that off the table, all sorts of wacky hijinks can come up. And just because you're immortal doesn't mean you can't be contained, enslaved, or otherwise 'dealt' with.