The Signal Men are giant robots created as advance scouts for an alien race. Their function was to track the progress of a civilization and then summon their masters when it had grown to a certain point. When their masters died, the Signal Men were left dormant underground on a variety of worlds. Peraxxus discovers them and becomes their new master, using them to destroy planets and sell them for scrap. Eventually four Signal Men wake up on Earth. They begin wreaking havoc on the planet while Peraxxus is alerted. Justice League International investigates their threat and tries unsuccessfully to fight the robots. They are able to defeat Peraxxus, and Rocket Red reprograms the Signal Men to stop destroying Earth.