Who is the faceless salesman that sales us our weapons of untold power for some warm coins? What do we know about this agent, able to appear and disappear from the tower? This enigma of a traveler? Tell me who you think He is in your reply, but my theory goes like this:
Xur says that "some of his cells started on Earth" so he was Human at a point, but he is not anymore. He is regrown, as the Nine can change strange coins into cells, much in the same way Glimmer becomes Energy. He travels obtaining
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basically like a vampire but instead of blood, coins.