I imagine a 1940 Ace Publishing Company editorial conference on the creation of Super-Mystery Comics. Men smoking cigars, jackets off, wearing white shirts and suspenders to hold up their pants are kicking around ideas for superheroes. Someone says “a magnetic guy.” But what would be his origin? How did he get those magnetic powers? Well, who cares? It's a comic book, and they are flooding the market so let's get it out now and worry about the details later.
That is just from my imagination, but what I understand from Toonopedia is that Paul Chadwick, who created and wrote Secret Agent X pulp stories, also wrote the story of Magno, the Magnetic Man. Chadwick used as its basis a story he wrote in 1934 called “The Octopus of Crime,” starring Secret Agent X.
In future issues Magno got a boy named Davey to help him. In this first story Magno is alone, yet up to the task. The artist on the story is unidentified.
From Super-Mystery Comics Volume 1, Number 1 (1940):