Metallo

Metallo is a radioactive cyborg intelligence who depends on Green Kryptonite as his energy source.  He is a former soldier who was used in experimentation by the United States Army,  eventually giving him the ability to project his consciousness into any technological device.

First Appearance:  Action Comics #252 (1959)
Creators:  Robert Bernstein,  Al Plastino
Powers:  Cybernetic Enhancement

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Issues

Black entries are ongoing series
Green entries are Limited series
Red entries are One-Shots
Orange are alternate universe stories
Blue is for comments

Reading Order

Action Comics #252 – First appearance of Supergirl, Metallo

Superman #423 – Whatever Happened to the Man of Tomorrow?

Superman Vol. 2 #1 (1987)
Superman Vol. 2 #2

Adventures of Superman #441

Superman Vol. 2 #20

Superman: Secret Origin #6

Superman #651

Action Comics #851

Action Comics Annual #11