I don't see enough evidence that the player wrote this terminal. It frankly doesn't make sense: why would you leave a cryptic message for yourself in the middle of nowhere? When would you have written this, and how did it get in a long-forgotten underwater Lh'owon terminal of all places? And why would you write it; who would you hope to see the message? Yourself? That only makes sense if you forgot your past at some point, and later went back in time to leave yourself a message, which while certainly possible given Marathon's story, is unlikely to happen just for the purposes of a single terminal. The only thing going for this argument is the Roland-Durandal link, which ties the writer to Durandal, but you're certainly not the only one who's tied to Durandal. Let me re-post my analysis of this terminal:
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OC AN If you return to the first terminal you get a garbled, but readable message. I read the formatted version on the story page, and before being influenced by other people's theories, my thoughts are thus: in a nutshell, the author laments a cruel, violent lover named Lethe, whom the author realizes does terrible things but seems incapable of losing as a companion. The two of them at one point went on a destructive, stormy rampage.
The author and its lover seem to have godlike powers: setting trees and lawns on fire, turning granite monuments to powder, and such. This makes the Jjaro the best candidate for their identities. Since there are two of them, and they met "at the beginning of the world," it really sounds like these Jjaro are, specifically, the same Yrro and Pthia mentioned in S'pht mythology. The author is Yrro, and Lethe is Pthia. The terminal says they change names, but Yrro has already been identified as masculine, and Lethe is identified as feminine in this terminal. Both the characters throw the world they're on in chaos. I believe the W'rkncacnter, presented as the force of chaos in S'pht mythology, is to blame. It supports the theory I made back in Six Thousand Feet Under: that rather than attack Yrro or Pthia directly, the W'rkncacnter drove them to madness in a 'devil-made-me-do-it' way. Since we know Pthia died as a result of the two encountering the W'rkncacnter, we may surmise that Yrro killed Pthia. Perhaps Yrro was so distraught when Pthia/Lethe started destroying the trees, lawns, flagstones, and such, he saw no other recourse than to stop her by force. He definitely seems as anguished as he does in the S'pht creation myth, calling Pthia/Lethe "drenched in my blood forever."
What doesn't make sense are the specifics. Who wrote this terminal? It describes things like granite and trees, but also specifics like "lawns," "flagstones," and "oaks." There are no oak trees on Lh'owon! Not to mention the human-created legends/epics of Roland, Beowulf, Achilles, and Gilgamesh. So there is a human influence there somewhere. The text appears in green, which is normally used by Durandal or the humans (and everyone in Marathon). It would seem someone has 'humanized' the text, to tailor it for human reading. Perhaps one of Blake's men stumbled upon it and, in the process of translation, substituted various Earth-specific nouns. By saying the writer has been called hundreds of names, it seems to be saying it is more of an idea than a person or being.
OC AN Now, after reading the section on the story page about this...they bring up several works of literature containing similar words or ideas, but these are not self-contained within the Marathon universe. While the story might be influenced by this or that, I'm still pondering the big question: who are the two subjects in the terminal?
So, I find it most likely that Yrro, the Jjaro, wrote this terminal. Therefore, since Yrro has been called Roland, the only one who may be controlling Durandal is Yrro. That makes sense to me, as the Jjaro are the gods of the Marathon universe, only arguably equaled by the W'rkncacnter. Durandal consistently seeks to gain the knowledge and power of the Jjaro, so it is consistent for him to ultimately be a 'tool' of the Jjaro.
So why does the terminal appear at this place and time? I think the answer has to do with Thoth, as this is the level where Thoth fully comes to life, and I'd stipulated earlier that Thoth is Jjaro-derived. Thoth, like this terminal, makes reference to Earth-specific things.
Now that I look at it again, one could make the argument that the female in the terminal is not Yrro's lover Pthia, but is the W'rkncacnter itself. I'd still give the edge to it being Pthia, though.