One of the most popular concepts in crime fiction of the 30s-40s was a policeman who felt too constrained by the letter of the law and decided to take up a masked identity to "serve justice rather than the law"!
Every rank from beat officers (
The Guardian) to police commissioners (
The Whisperer) donned a mask (and usually a skintight outfit) to fight criminals in their off-duty hours.
One of the longest-lasting was 
Officer Dan Garret aka 
The Blue Beetle.
Garret had good reason to be disillusioned about the power of law and order.
His late father was a police officer killed by a criminal who evaded prosecution even after 
Dan himself joined the force.
Seeing the fiend go free due to an unbreakable (though false) alibi, 
Officer Garret took matters into his own hands.
Donning a mask, fedora and business suit (ala 
The Green Hornet), 
Dan adopted the 
Blue Beetle identity to harass the felon and force him to to commit a crime in front of witnesses, including 
Garret's reporter girlfriend and her photographer!
It worked, and undeniable retribution was finally delivered to the killer!
In the next issue, after saving scientist Dr Franz, from racketeers, the grateful chemist gave Garret a suit of bulletproof chainmail, as well as a supply of an experimental vitamin, 2-X, to enhance his strength and reflexes!
Combined with a pair of lethal .45 automatics, that chainmail and "power pills" made the "upgraded"
 Blue Beetle a formidable foe indeed!
The Beetle's adventures began in Fox Comics' 
Mystery Men Comics #1 (though he didn't make the cover until #7) and ran thru all 31 issues.
He gained his own title 
The Blue Beetle, which published 60 issues between 1939 and 1950 and also appeared in 
every issue of 
Big 3 Comics, an anthology title featuring the most popular characters from Fox's various titles!
Blue Beetle was popular enough to be the 
only Fox Comics character to warrant both a newspaper strip 
and a dramatic radio series, both of which were, regrettably, short-lived. (The newspaper comic strip featured art by a young Jack Kirby!)
In the mid 1950s, another publisher did a reprint series which proved so successful that they published a reworked new version of 
the Beetle that ran into the 1960s, was revived again in the 1980s and runs on-and-off to this day. (In each of these revivals, 
the Beetle has a 
new secret identity and powers.)
But 
Dan Garret, the original 
Beetle, hadn't been seen since the mid '50s, until 
Alex Ross
 revived him in the acclaimed 
Project SuperPowers
 in 2007!
Atomic Kommie Comics™  has also revived 
The Blue Beetle as part of our 
Lost Heroes of the Golden Age of Comics™  line with 
several of his best covers from his own title and 
Mystery Men Comics on t-shirts, mugs, and other goodies.
Heck, we're so proud of him that we gave him 
his own 12-Month Calendar with a rarely-seen Golden Age comic cover for each month!
FREE comic convention season bonus: mp3s of 
The Blue Beetle radio show!
And BUY 
Project SuperPowers
, the BEST Golden-Age revival comic (er...graphic novel) out there!