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?
Edited: 7/29/2014 4:43:05 AM PermalinkIm pretty sure in some dialogue it said we(humans) built them. edit from the wiki: [quote]Exo began as self-aware war machines developed by humanity during the Golden Age for a long forgotten war, with the sole purpose of protecting their creators. They were rebooted during the collapse and now have no memory of their original function.[/quote]