The original Golden Age Blue Beetle was Dan Garret, son of a police officer killed by a criminal. This Fox Features Syndicate version of the character debuted in Mystery Men Comics #1 (Aug. 1939), and began appearing in his own 60-issue series shortly thereafter.
Rookie patrolman Dan Garret donned a bulletproof costume (described by Garret as being made of a chain-mail which was "as thin and light as silk"), and temporarily gained superhuman strength from taking the mysterious vitamin 2-X.
The supporting cast remained fairly stable throughout this original run, and included Joan Mason, a crime reporter for the Daily Blade who would ultimately star in her own backup stories, and Mike Mannigan, Dan's stereotypically Irish partner on the force. Dr. Franz, a local pharmacist and inventor of the bulletproof suit and 2-X formula, played a large role in the first few issues, but eventually faded from the cast.
A popular character of the era, he had his own short-lived comic strip, drawn by Jack Kirby (using a pseudonym) and others, and a radio serial that ran for 48 thirteen-minute episodes. When superheroes fell out of fashion in the late 1940's, Fox downplayed the Beetle's superheroic aspects (his superhuman abilities were removed) and eventually relegated him to a host for true crime stories before the character went on hiatus.