Johnny was a henchman of Mr. Freeze.
Johnny helped Freeze during a break-in at a warehouse. Unfortunately, he got in between Freeze and Batman, and with his legs frozen, he was left behind. Batman blindfolded him and took him to the Batcave, where he was put in a special healing tank. Batman managed to successfully thaw out Johnny's legs. Johnny repaid Batman by giving him intelligence about Mr. Freeze and handing himself over the Gotham Police.