- To use professional terminology, this was a man who is "Going through it.".
Once a regular man named Dan Dyce, he had the misfortune of looking identical to his scumbag friend, Jacob Horn. Jacob did a crime and was about to get arrested, which sucked for him because Jacob really wanted to see his wife give birth to his son. Dan, being the lovely, well-meaning fellow that he was, offered to take his place in the prison.
Unfortunately, Jacob died, so Dan was just stuck in Prison... or, well, he would be, but he managed to tunnel out of Prison... but he felt bad about escaping, so he just immediately went back to jail. But, y'know, he spent all that time digging an escape tunnel, he may as well use it, so he donned a fancy costume and decided to become a vigilante named 711 (that number being his prisoner number).
Now, personally, I have some concerns about his plan. Being a 1940s hero, his main opponents were gangsters... and a guy named Brickbat, who wore a Batman mask and killed people with bricks. Still, violent criminals here, and he'd beat them and get them arrested and... well... presumably they're close to his prison, so when the criminals get arrested, they're in the same prison as him. And his superhero persona is named after his prisoner number. And he doesn't wear a mask. And he has this tendency to walk by smugly once the criminal arrives at the prison.
At this point, you've got to wonder how this guy is still alive, and the answer to that is quite surprising: he isn't! That's right, in his short run of comics, he canonically gets killed off permanently by a mobster named Oscar Jones.