User blog comment:B1littlehero/Speculation of the Origin of Species/@comment-24013204-20140611172200/@comment-160529-20140611220126

"So, where does that leave the Vex? It's clear they aren't fully robotic, like the Exos, but were they created by Humanity as well in some different time (at least originally), or are they the product of aliens? Or maybe even the ultimate synthetic army of the Darkness itself? Who knows? Only Bungie does. "

I outline my own theory on the Vex further down, I really do honest to god believe they are from the distant past on venus... and that they are trying to bring their creators to the present, that their agreement with the darkness is to allow them access to its power to better help them warp time.