So today is xürsday and on this special day we, the guardians, get a special visit from a certain entity. Xür (AKA agent of the nine) comes and goes freely, as described in his menus screen. However knowing who he is has a different meaning then knowing WHAT he is. It is my belief that xür is a taken guardian, of some sort. Let's address the first part of my theory, regarding the taken part. So a quick briefing for those who don't know, taken are dead or once alive beings that have been corrupted completely by the darkness/deep. These "taken" Tend to be black and white with a flowing texture on their forms. Alongside their flowing skins, the taken twitch in a nervous manner that tends to be unsettling. Xür has rapid and quick movements, similar to taken that us guardians fight. Xür also has his face tentacles that are white/grey tipped and black at the base, similar to taken. Also, xür's character figure (the actual in-game avatar) is just a black face with golden eyes, although this does not support the theory but I still find it interesting. Now, we move into the second portion of my theory, he might be (I think he is) a guardian. If you pay attention to xür's right arm (the players left hand side of the screen) he has a bond that is similar to a warlock bond. Now I know that warlock bonds go on the left arm but if he is taken then it could always switch sides, or it shows disassociation with the tower. I also know that there is taken armor but that is only taken essence applied to pre-existing armor and not actually be transformed by the darkness/deep. I know this is not much to go on but I firmly believe xür is a taken or corrupted guardian, to an extent. I'd love to hear your thoughts and feedback in the comments section down below!