I would like to think that it's Arthor Amhrad, the Chapter Master of the Astral Knights, who all died destroying the Necron World Engine. That story always inspired me and I would like to think that at least one of them made it out alive, even as a prisoner.
This. I think this is the most interesting and entertaining possibility. I like to think he saw some horrific experiments deep in the bowels of the World engine that explain his contorted face.
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