Edited: 7/29/2014 5:05:24 AM PermalinkMy friend asked about this. Now it's a long shot of a guess. I told my friend, that people on the forums call EXOs Terminators... now maybe cliche, but what if that's not too far from the truth? Say, the Fallen, made the EXOs. VI infiltration units, created to assassinate high ranking humans during the war. And "protect" their creators, maybe as said the Fallen? However, they became full blown AIs, fully self-aware, because of the Traveler. It gave them "Free will", to decide if killing humans (Awoken) was really the right thing. Just my thought.
Hopefully in the story, or sidequest, or a dlc I don't care which we get to find out who built the exo. Maybe a counter force anpgainst the Vex? A weaponized ghost companion? Souls of those returned from the void?