The H.U.M.A.N. (Humanoid Utilized Mechanical Android Nomad), using the alias "Michael Artaxerxes" was an artifically created human-robot, fusing synthetically grown human tissue and state-of-the-art technology, the same used to create Ellie Bates' C.L.A.W. 'He' is a sleeper agent, not fully knowing of his true origins, even starting a relationship with Bates, frequently experiencing black outs and mild amnesia. It was later revealed that he was 'the creature' that attacked Captain Bates' team in Scotland and severed her hand.
Once he knew of his true origins, and that sinister scientists abusing the alien technology given to them while working in U.N.I.T., he eventually went completely insane and tried to even find a way to kill himself. In order not to 'damage the equipment', he was then remotely reprogrammed and went into his primary function, losing any humanity whatsoever and becoming a mindless tool.