There have been a good few theories on who the Exo Stranger is and what her ultimate goal is. Here's my theory. First, let's start off with the Deep Stone Crypt, the infamous subroutine that seeded the first Exo consciousness. The Deep Stone Crypt mark, along with the description of the Crypt and its surroundings, resembles the Citadel quite well. This leads me to Maya Sundaresh. Maya was part of an Ishtar research team who studied the Vex. She and her team became stuck in a Vex simulation, enlisting the help of a Warmind to get out. They managed to save 227 identical copies of themselves from Vex hell. With the help of biomechanical proxy bodies, a the Warmind, and a neural firewall, they approach the Citadel, ready to release their copies into the Vex networks and see what is on the other side. Maya Sundaresh, who is oddly quiet, says some odd things. [quote]"What could you do with it?" she murmurs, staring up. "If you understood it?"[/quote] [quote]"Maybe you could bring something back to now. Something you needed."[/quote] [quote]"Or go forward and learn something vital. If you knew how to control it, how to navigate across space and time."[/quote] The team then release the copies into the vast networks, hoping that they will come back with knowledge. I believe Maya ponders on this, and at a later date (possibly the Collapse), she returns to the Citadel in her proxy body and enters. She sees the Collapse, the rise of the City, the Great Disaster and Twilight Gap and the Reef Wars. She witnesses what will happen to humanity unless she steps in. So she travels the dimensions, looking for the right universe where the right Ghost raises the right Guardians who finds just the right jumpship to get to the City. [quote]This is where I always choose to stand. I put my feet where I put my feet before and where I will again and I look at the sky. I always stand here, resolute. Then fall back to that point, there, where everything shatters... There are always the dead. Their names shift. Sometimes I think I see myself among the dead. But I am resolute.[/quote] She watches you as you fight the Fallen, the Hive, the Vex, and the Cabal. She knows what is to come, and she now knows that you are the right Guardian to save humanity. It is possible that she is still tethered to that Venusian Warmind back in the Ishtar Academy, or perhaps she carries him/her with her. I think she is talking to the future version of your Guardian on the Stranger's Call mission, which would explain the Ghost-like transmat. Of course, this may be simply the ramblings of a madman [b]TL;DR[/b]: Maya Sundaresh is the Exo Stranger