The word you are looking for, friends, is "Astronaut."
Wearing pilot goggles, leather jacket, and a long red scarf, The Astro-Naut made no pretense for a secret identity. He was testing rocket ship engines in flights over the city. Everyone knew him by his name, Roy Virgil. They also knew he was a bit eccentric, very wealthy, a visionary. His passion for traveling to space gave him the nickname, The Astro-Naut. That become his calling card.
During the Great Depression, organized crime families in Romeyn Falls dug themselves in, diversifying their operations. In 1936, the Ingels Street mob tried muscling in on Roy's work, demanding protection money, and he refused. They sent round the Convincer, a one-man wrecking crew, to convince him, but Roy took care of him, dropping him off with the police to tell them about his bosses.
Councilman Joseph Greenwald visited Virgil Air Systems afterwards to see if Roy was interested in taking up crime-fighting, if perhaps the city could support him. Joe helped Roy with his business, permits, and such, and in return Roy helped him campaign. Perhaps it was Joe who got Roy into costume, perhaps not, but he started showing up in a stylized astronaut outfit.
As Roy made good on his arrangement with the city, taking down criminals, his reputation grew - there were newsreels, magazines and toys, and they even started making a movie about him.
His development of the Ethero-Drive, which allowed him to slip through folds of empty space, was a big breakthrough for him, allowing him to venture out into the universe, where he fought villains, had adventures, and encountered alien civilizations. Inspired by the technologies he saw out there, when he came back to Earth he'd work on inventions that would do the same thing, or do entirely new things born of new knowledge.
Along the way, he met Xalzana, the one woman he might have left Earth behind for, but though they met numerous times, and something he thought was love developed, there was a fear in her, not of him, but of something she wouldn't say. On the night he intended to propose to her, there was an attack, separating them, and though he searched more than a dozen worlds for her afterwards, he never saw her again.
Around 1942, Roy came across a star system under attack from the Mrevani, a ruthless race bent on conquest. He discovered that when the Mrevani had first been visited by interstellar explorers, they'd killed them and taken their technology, turning their warlike ways out towards the universe at large, attacking everyone they met. They'd got the technology before they were ready to handle it, and Roy feared that if he gave humanity that technology, then they'd end up going down a similar route. Shaken, he withdrew from human society, becoming a recluse; when the American goverment came round, looking to use his inventions in the war, he refused.
The refusal shook people's faith in him. Though he still did his own part for the war effort, at one point getting captured by the enemy and escaping, the American public preferred to forget about him, turning to heroes who were more clear-cut, heroes they could be certain of, and he disappeared from view.
In late spring of 1946, the Mrevani came to Earth, laying waste to Romeyn Falls. The Astro-Naut returned to stop them, a fleet of drone ships with him to defend his home city. Deftly avoiding the Mrevani's attacks, he piloted his ship into their flying base and blew it up, but took serious injuries in the process. He used a teleporter to return to his base in Romeyn Falls, the Gernsback Building, and with Joe's assistance destroyed his remaining work in order to avoid anyone else using them. Once that was done, he used the teleporter once again, but where he went, whether he lived or died, what ultimately became of him, no-one on Earth knows.
The town renamed itself in honor of his bravery, becoming Astro City in 1947. The rocket beacon on AstroBank Tower was reconfigured, becoming a warning signal, alerting heroes of impending danger.
Roy had a once-in-a-lifetime mind, coming up with inventions far in advance of Earth technology at the time. As Joe put it, Roy made breakthroughs practically by force of will, simply by knowing they were possible. He doesn't seem to have realized he was anything exceptional, assuming anyone could do it if they put their mind to it.