Analysis of the corpse shows it is young, which is completely inconsistent with a man who was supposedly born several centuries ago. Influence of the Shadow, or something more trivial? The numerous Regeneration Chambers and the detailed medical data on Knights of Cydonia that we've found at Thule HQ points to a possibility of cloning. Whatever the case, one thing is clear: the body was heavily modified by some form of Shadowtech to receive mystical energy from a massive array of human minds, for the purpose of mass neural destruction. Thankfully, the nature of Shadowrealm we've fought him in apparently made this ability impractical to use.