It could also be her boss he's talking to (Destiny)

by Xenos , Shores of Time, Wednesday, September 23, 2015, 15:22 (3138 days ago) @ Ragashingo

Why? I don't remember the Exo Stranger or any of the Ishtar scientists being mentioned near Osiris, which could be his connection with a Warmind. Am I forgetting something?

In the Osiris Grimoire card someone claims to have proof that he was a Golden Age experiment mis-incarnated as a human. The reasons I think the Exo works for Osiris are because:

1. They both have an obsession with the Vex and are working outside of the City's influence to accomplish their goals.
2. The Exo stranger has a pulse rifle that looks identical to the Fate of All Fools, which was originally the reward for going 9-0 in Trials (in data mining).

Not that this proves anything, but I even asked a Bungie employee if the Stranger did work for Osiris and they told me that was a great question, but wasn't drunk enough to answer it :)

P.S. This doesn't discount the Maya/Stranger theory, could be a further piece of the puzzle. I think if both the Strange and Osiris are obsessed with the Vex they would probably be linked in some way.