I always assumed the speaker is the silencer of the traveler. Many before him wore the mask to keep anonymity, but who's to say he hasn't been the same speaker all along. There was concept art for the darkness as humanoid figures likely they can bind themselves into any form. His whole body including his hands are covered, on top of that you see gaps in his face mask yet there is no face showing. What could he be, for some reason he always seemed evil, and I could never quite place it. Maybe it's my inner punk saying -blam!- authority especially when it uses such enigmatic forms of communication. Perhaps the other races maybe minus the hive were running from the darkness, and sought refuge in our solar system. Maybe they thought no one was in our solar system, or maybe they didn't care and wanted to wipe us out and take claim to the last safe haven from the darkness. The hive are also the only race the ghost speaks of having been allied with the darkness, he doesn't speak fondly of the others but regardless there not spoken of being a lied, not even the vex. Which the stranger speaks of as being evil so dark it despises other evil, perhaps they want revenge against the darkness, and consume all life to attain there goal. It would seem they are out for blood, what was it they were even worshiping in the black garden, or maybe they got pissed at the traveler for forsaking them or something, and want revenge on it. Either way I feel that the speaker is the one pulling the strings for this war, and that he for whatever reason is not all that we can see. He may not even be completely evil, revenge can corrupt even the kindest souls. I think this story will be filled with many moral greys. Evil isn't usually born, it's almost always created.