Michael Mason was just a normal guy before the incident. He worked, payed taxes, he even helped the little old lady across the street with her lawn work during the summer. His simple life was a good one, and he was happy. Unfortunately he didn't live in the best of neighborhoods. He was jogging home early one grey morning, when a group of local thugs fell in behind him. Picking up his pace, he ran for as long as he could.
Finding himself out of breath on Carson's bridge overlooking the river, he backed away from the group so intent on catching him. "Give us your money and keys," they said, "and you won't be hurt." Michael put up a short lived fight, and one of the punks stabbed him in the side during the struggle. Grabbing his keys, wallet, and phone, the group rolled him over the railing into the river.
Bleeding out, Michael floated down river, finding himself nearing the docks, and the ChemTech R&D plant. They were dumping in the water, but he wasn't conscious of it. Darkness clouded his mind as his blood mixed with the river water and dumped chemicals, which he later found out were tied to the development of an experimental morphic steel.
He was lucky enough to wash ashore about a mile out of town, among trees and away from the road. This was quite the break because parts of his body where changing, shifting from flesh and blood to metal, and back. With time, and concentration, he found he could transform his entire body into a silvery living steel. This gave him incredible strength and neigh invulnerability. It took some days out in the wild before Michael had gained control of the shifting process, and felt he could return to civilization.
After dealing with the thugs that accosted him, and nearly cost him his life, Michael quit his job and abandoned his old life. Taking the name Chromium, he decided to try the mercenary route. After a few jobs for some rather distasteful men, he realized he just couldn't do this kind of dirty work. He found Hero Inc, and offered his strength to their team, hoping for a better way to earn money adventuring.