Someone has gathered the various facts about TNO's history throughout the game and has combined them into this. It may shed some light, though of course the original crime is never actually stated. Also MCA probably didn't really get Fairfax's question, since it was about TNO's original crime before he became immortal and started having incarnations. Or he just didn't remember and dodged it
found in:
http://bootstrike.com/Torment/Online/tti4.php
History of the Nameless One
The following was found on a sheet of vellum shuffled in among a manuscript of Candrian's On Planar Travel bought in the Clerk's Ward. It is a history, believed written by one of his companions, of the man known by various names, but most commonly as the "Nameless One" in Sigil.
What of the original incarnation? There was an advisor, whose lying advice wrought betrayal. Hints of a contract signed. A crime was committed, one so awful the acts of all future incarnations are as nothing compared to it. The crime itself is unknown, save the implication that the planes are still slowly dying because of it.
He sought help of the night hag Ravel Puzzlewell, to grant him immortality, so he could escape his punishment and perhaps atone for his crime. And for love of him, Ravel granted his request, stripping his mortality from him. But a dreadful price was paid, since although the death of the body was no longer permanent, it did injure the mind, and memories were forgotten. Thus were born many incarnations, each starting with only fragments of memory of past existences.
There is also a sliver of another memory of Ravel, which seems to tie in with the myth of the three wishes. In the myth a man wishes for the awful knowledge of who he is. Perhaps this refers to a time when the original incarnation realized the full extent of his crime, and what the punishment must be?
There are only fragments from the many incarnations which followed. General of armies, a mage trained by a puissant sorcerer, a bloody-handed criminal chased by the mercykillers, a thief reduced to skulking beneath the streets of Sigil. Wandering many planes, acts of cruelty and kindness, chaos and law. One constant was the symbol of torment on his body, which drew other tormented souls to him. And many to their doom as well, no doubt.
At some point an incarnation which knew of the Fortress of Regrets, more accurately the Fortress of His Regrets, had a conversation with Trias the deva in which he described what he knew of the fortress.
One incarnation lead a revolt in what was then the prime ward, opening all the gates in the ward to the lower planes using an artifact known as the Shadow-Sorcelled Key. The Lady of Pain finally crushed the revolt. Could his scarring be explained by having fallen under the Lady's shadow? Could even an immortal survive that?
Several centuries ago Ravel attempted to open all the portals in Sigil. Whether it was to prove she could solve any puzzle, or as she later claimed to free the Lady from her cage, the Lady mazed her, removing a source of knowledge from access by later incarnations.
More than 200 years ago an incarnation was a member of the Sensates. Apparently this was a happy time for him, but he disappeared, with only rumors of his murder following in his wake.
At some point after this was the time of the 'practical' incarnation, who, but for one, came closest to defeating his enemy. A cold, ruthless incarnation. He kept detailed notes, and had tattooed instructions on his back to future incarnations. He tricked Pharod into a quest for an object he could not be bothered to find himself, and imprisoned the mercykiller Vhailor in a cell only he could release him from merely on the chance that Vhailor's abilities might one day be of use.
He commissioned a dream machine from Xeno Xander, to force the dreams which he could not have. He also commissioned from the Godsmen a portal to reach Ravel in her maze. In the end, he did not have time to make use of either item.
He attempted to thwart his unknown enemy with false bodies, by hiding on outer planes, even building a tomb which was both a trap for his enemy, and a repository of knowledge for future incarnations.
Nothing he could devise could throw off his enemy, so he decided to seek his enemy in his lair. To that end he gathered companions to himself.
He sought knowledge from the pillar of skulls in Avernus, and freed one skull from the pillar who he named Morte. Then he nearly killed the skull when it could not answer his questions. Unfortunately Morte still cannot wholly escape his past, and embroiders the truth. Thus he is not a very reliable source.
He tracked down a githzerai named Dak'kon in Limbo, because of the Karach blade he wields. He saved his life and gained his sworn service by cynically offering the words of Zerthimon. Words which meant nothing to this incarnation.
He enlisted a blind archer, Xachariah, one who could still see by other means, and whose arrows always found his enemies' hearts.
He professed a false love for Deionarra, so he could bind her and make use of her abilities.
Finally, a little more than fifty years ago, he and his companions traveled to the Fortress of Regrets, to scout his enemy, his Mortality. The first part of his plan went well. Deionarra was allowed to die, her love for him anchoring her to the fortress in death, and her powers gaining her insight into the fortress that no other could have provided.
Otherwise it was a disaster. He and his companions were separated. Dak'kon and Morte managed to escape, although wounded in faith and courage. Xachariah and the 'practical' incarnation died, although their bodies returned to Sigil. Possibly his enemy, after defeating him, transported him back to Sigil before killing him for fear that his dying in the fortress would be the end of himself as well?
What was likely the next incarnation was insane, quite likely because of his experiences in the Fortress of Regret. In his insanity he viewed his other incarnations as his enemies, as body-thieves. Although only extant for a few years, he was not unclever.
He destroyed his previous incarnation's laboriously constructed journals, a great loss, hardly balanced by the maunderings he inscribed in his previous incarnation's trapped tomb, and his own rambling journal. He also tried to burn the legacy left by this previous incarnation with Iannis the Advocate, but failed.
He left many traps for his other incarnations, the most devious of which was a sensory stone in the Festhall with two experiences, one overlaying another, the second a snare which only another incarnation could trigger.
He kept a journal, written in the tongue of Uyo, a tongue he guaranteed no one would be able to speak by murdering his teacher, Fin Andlye. This was not enough protection, so he required opening a puzzle box to access its contents, and trapped it besides.
This incarnation was also responsible for an amazing discovery. He found someone who told him his mind was weakening with every death of an incarnation, and who, somehow, was able to prevent memories from slipping away upon death. Unfortunately, this discovery would only benefit a future incarnation. Predictably, the 'insane' incarnation butchered his helper.
In fact, this incarnation viewed anyone who seemed to recognize him as a threat, and threats were all too easily eliminated. Even being mazed by the Lady did not stop his rampage, since he managed to escape his prison. His murderous fury was finally quenched when he met unexpected resistance from one of his victims, and plummeted to his death. This was roughly fifty years ago.
Of the next few incarnations little is known, although one was a powerful mage, and tutored an apprentice named Ignus who loved fire.
Finally there is the last incarnation, who awoke in the Dustmen's Mortuary, the one whose memory is not veiled at death. Curiously, the person who found this incarnation's body and took it to the Mortuary was drawn to the remains. How drawn? Was it Fell? His enemy? Possibly even the mark of torment, drawing another tormented soul even in death?
This last incarnation set out on a quest to backtrack figures from his past, a path which eventually led to his enemy, his Mortality. This was mirrored by his enemy's desire that he follows the path, so that remaining clues to his enemy's location could be eliminated.
He fought Ravel, Trias and his Mortality. He also faced three of his former incarnations. Interesting examples of the Rule of Three.
He and his companions defeated his Mortality, and undid the separation which made him immortal so long ago. His long delayed punishment caught up with him, and he was sentenced to serve in the Blood Wars.
