The Transcendent One's identity is not known for certain until the very end of the game, although someone has left behind a trail of missing documents and much subterfuge in the service of covering up the existence of some adversary, along with all evidence of The Nameless One's past. A similar trail of Deaders, such as the fathers of Finam the Linguist and Hamrys, and Ravel herself, attest to the ruthlessness of this killer unknown. It's also implied that he destroyed or ordered the destruction of all the heads on the Pillar of Skulls who knew of his existence.
The Transcendent One is the The Nameless One's mortality in a corporeal form, separated from The Nameless One by his request. Only Ravel's power was sufficient to enact the ritual which cursed The Nameless One with immortality.
He believes that nothing can change the nature of a man.
The mortality manifested into physical being and evolved, growing in power and intellect. The Transcendent One (TTO) and The Nameless One (TNO) share a bond, and if either of them dies permanently, so shall the other. Unlike TNO, the Transcendent One remembers the past lives that both shared - and retains all of the powers and skills gleaned from them.
Later he reveals that he sends out shadows after TNO not to kill him, but rather to make him forget through his death, and therefore leave the Fortress of Regrets (and the Transcendent One himself) in peace once and for all.
He is the keeper of the Fortress of Regrets, which dwells in the Negative Material Plane. The Fortress is formed by the regrets of the Nameless One and the shadows that haunt the empty halls are victims of TNO's life-leeching "immortality". The Transcendent One claims that the Fortress is his home, that he sustains it, and wishes merely to live in silence within its walls. However, despite the all-powerful and all-knowing abilities of the Transcendent One, he cannot leave the Fortress (and the Negative Plane) for extended periods of time.
Through dialogue, it becomes clear that the Transcendent One is very much a prisoner of the Fortress. As the TNO suffers the deaths of the mind, the Transcendent One suffers the deaths of the body (due to their shared bond). Little by little, the Transcendent One is getting weaker to the point where he needs the Fortress's energies to sustain him, not the other way around. The Transcendent One has weakened so much that he needs to wear his hated nemesis Ravel's black-barbed frame to maintain his power. Despite the barbed armor and the Fortress' energies, the Transcendent One is doomed to a slow oblivion. The Fortress of Regrets will be his prison and eventually his tomb.
The final conflict between The Nameless One and The Transcendent One can be resolved entirely through dialogue.
The Transcendent One is voiced by Tony Jay.
TNO: Why is sustaining this place so important for you? If you are truly as powerful as you say, why would you want to remain here? There is NOTHING here.
TTO: IT IS MY FORTRESS. IT IS MY HOME.
TNO: And what a home it is, too. Mortared from my regrets, with nothing but the shades of those we've murdered filling its halls, abandoned relics of the past languishing beneath dust, and the life-draining energies of the Negative Material Plane to feast the eyes on. There are words for places like that - they're called *prisons*.
TTO: EVERY WORD BETRAYS YOUR IGNORANCE, BROKEN ONE. THE FORTRESS IS *SILENT*. ALL THAT COMES HERE *DIES* BEFORE INTRUDING INTO MY PRESENCE. AND THE SHADOWS ARE QUIET CREATURES.
TNO: I think you *have* to remain here, along with the shadows and the ghosts, because that's what you've become. I don't think you sustain this place at all. I think it sustains *you*.
TTO: I REMAIN HERE BY *CHOICE*.
TNO: *Really*? So when you said you can't journey beyond this Fortress for long, you were lying? And how is it possible that a Fortress built from MY regrets needs YOU to sustain it?
TTO: I WILL SEE YOU DIE A *THOUSAND* DEATHS FOR YOUR INSOLENCE, BROKEN ONE. YOU ARE AN INTRUDER WITHIN THESE HALLS, AND I SHALL SEE TO IT YOU *NEVER* RETURN.
TNO: Consider this: you say we are linked. So when I suffer, you must suffer as well. Perhaps you are trapped here *because* you suffer, but differently than I do.
TTO: WHAT IS THIS FOOLISHNESS YOU SPEAK OF?
TNO: Is it possible that as I die the death of the mind with each of my deaths, you die the death of the body? As I lost spirit, you lost substance. That's why you find it harder and harder to leave this Fortress and travel beyond this place. This Fortress is not only your prison, it's going to become your tomb.
TNO: Is it? You said we were linked. Surely, you've felt your body wane over the past century - you even carry the branchings of Ravels' frame over yourself, and you *detest* her - but you need the frame over your spectral form to prevent yourself from decaying faster.
TTO: EVEN IF THERE WERE TRUTH IN YOUR WORDS, THERE IS NOTHING TO BE DONE. I WOULD SOONER DIE THE DEATH OF THE BODY HERE IN THIS FORTRESS THAN SUFFER EXISTENCE WITH YOU.