Here's my theory. Shaidar Haran is first a Myrdraal, not a gholam or Jain Fairstrider. And is second, an avatar of the Dark One. Some evidence has been given before. He is a Myrdraal and not one of the other two options because: 1. He affects the one power differently than gholam do. 2. He can jump through shadows which is a Talent only Myrdraal have. The forsaken don't even know how they do it, so they couldn't possibly give that Talent to their own constructs, the gholam. This evidence also eliminates the Fairstrider option, because Myrdraal can do what they do by birthright, their skills aren't learned. He is a manifestation of the Dark One because: 1. He is bound to Shayol Ghul. No other Myrdraal is bound in such a way. The only thing bound in Shayol Ghul is the Dark One. 2. His loyalty is beyond question. The spikes in the hallway down to the bore are a good 2 feet above his head, while they just brush the tops of the heads of the forsaken. The only thing the Dark One can trust completely is himself. 3. He can boss the forsaken around.