Capitan Europa is Captain Union, both the setting's Superman analog and primary antagonist.
Captain Union is the end result of a series of eugenic breeding experiments started by Enlightenment era alchemists to create the perfect man. Born Christmas Day 1900 he fought in WW1 as a teenage boy, then disillusioned by the war and the potential for destruction that superhumans like him had he used super hypnosis to make everyone-including himself-forget about the eugenics project.
He became a man without a past and roamed America like a superpowered Tom Joad as his powers crew. He was a socialist hero like the Golden Age Superman. He forced cruel mine owners to do their own work, rebuilt ghettos with his bare hands, protected unions from Pinkerton legbreakers, that sort of thing.
He became even more of a socialist after he befriended FDR, even wearing the Blue Eagle of the NRA as his emblem. At first he disliked the NRA's strict regulation of business but he gradually began to believe it was the right thing, and this paved the way for him thinking that government control is the solution to everyone's problems.
When WW2 broke out Captain Union became America's secret weapon against the Axis, but the old hero was haunted by flashbacks to his time in WW1. Although he tried his best to capture soldiers without killing them he couldn't help but claim more than a few lives.
During what he believed to an infiltration mission in Hiroshima to ready an Allied invasion of Japan a "communications device" attached to his backpack went off. It was the world's first nuclear bomb, and Captain Union was at ground zero.
Official history records the "Hiroshima Incident" as a desperate attack by Japan's superhuman Sun Lord to kill Captain Union.
And that's what everyone believed until Captain Union learned the truth years later.
Captain Union never forgot tasting the collective ashes of thousands in the air, and being alone with the unearthly quiet.