Mister Machine (serial number Z2P45-9-X-51, or X-51 for short) was originally designed to be a killer as part of a U.S. Army project to build robot soldiers. He had solar powered batteries built into his exoskeleton. All of the other robots in the series went insane after gaining sentience, while X-51, who has been called "the Robot with a soul", survived. He was raised as the human son of his creator, Dr. Abel Stack, who later died in an attempt to protect his "son". X-51 escaped, and was pursued by the government.
- 2001: A Space Odyssey #8 (July 1977)
- 2001: A Space Odyssey #9 (August 1977)
- 2001: A Space Odyssey #10 (September 1977)