Machine Man, whose real name is Z2P45-9-X-51, was the last of a series of sentient robots created at the Broadhurst Center for the Advancement of Mechanized Research in Central City, California, by robotics expert Dr. Abel Stack for the US Army. However, all previous 50 experimental robots went mad as they achieved sentience and became psychotic, due to a lack of identity. X-51 was the only survivor, as he was treated as a son by Stack and given a human face mask as well as being exposed to one of the monoliths from . After Stack died trying to protect him, X-51 assumed the human name Aaron Stack and escaped confinement, only to be relentlessly pursued by the army. X-51 named himself Mister Machine in issue #9 of the 10-issue run of "2001".