- "Metallo isn't just flesh and blood anymore. Cadmus has given him a metal endoskeleton."
- —Superman[src]
Metallo may refer to several characters, enhanced by the 'Metallo Protocol' with a Green Kryptonite heart:
- John Corben, a mercenary turned into Metallo by Project Cadmus.
- Gilcrist, John Corben's partner in the role of Metallo and originally a Cadmus scientist.
- "Metallo" a subject of the "Metallo Procedure".
- Otis Graves, a terrorist who was resurrected during the "Metallo Procedure".
- "Metallo", a metallic servant of the Nazis of Earth-X.
- Lena Luthor, a millionaire who was transformed into Metallo by Lillian Luthor in an alternative timeline.
- The Metallo Protocol, which is the process that implants a Green Kryptonite heart into the test subject.