Backstory: In the year 305 BC King Demetrius of Macedonia laid siege to Rhodes. History tells us that the Rhodesians eventually repelled him after a year of fighting, but as we all know, history likes to write off the fantastic. As the siege laid on, the Rhodesian's petitioned the gods for a way to break the siege. It was Helios, their patron who answered. He instructed the Rhodesians to craft a warrior of stone, and the gods would breathe life into it. They set to work, sculpting the ideal warrior, and when they were finished, they prayed to Helios again. He descended, carrying a beautiful diamond, and machera forged by Hephaestus. He placed the diamond within the statue's chest, and it closed around the gem. The statue rose, and Helios presented him the sword, and set him to the task of protecting the city. He explained to those assembled that Hephaestus forged the blade of their guardian, and Athena blessed him with the Aegis, making him nigh indestructible. From Ares he was given the soul of a warrior, Zeus the ability to change himself to be a greater warrior, and even Gaia had spoke, giving the stone warrior dominion of the earth itself. The siege would break, the people built a grand colossus to remind them of the giant warrior who had saved their city, as well as honor the god who brought them that boon.

But he was now an eternal guardian with nothing to guard. He stayed in Rhodes for a time, the people referring to him as the stone, or petra in Greek, and so he adopted it as a name, as humans had those and it made things easier. Eventually, he felt the mortals no longer welcomed him, and then he began to wander. Various sightings placed him throughout the Mediterranean, then Europe and Asia, until a sighting in the 1800s confirmed he had moved to the New World. He absorbed man's culture, and fought those who would hurt those who could not defend themselves throughout history, until World War I. He had joined with the Allies as they went to Gallipoli, and seeing the horrors of what men would do to each other in the name of their nations, after the war he left to the African continent, content to stay off the radar of men.

It wasn't until he was entreated by Hypolltya, Queen of Themysicra did he leave his homestead, helping the Allies in North Africa and Italy during World War II. Seeing more of the horrors humans were willing to wage on each other, he left again, this time heading deep into the rain forests of South America. What caused him to return to the world this time isn't certain. He says it was time for him to try and save as many lives as he can. Others suggest Diana of Themysicra asked him to return, to provide needed muscle to Batman's campaign. Whatever the case, he's joined Batman's cause in Century City.