Dual demented docs do doggedly devilish deeds! Say that five times fast! Or better yet, have the bad Doctors... Sivana and Spectro... of adjacent Earths S and 4 say that via their cloned proxies. Each of the good Captains... Marvel and Atom... faced off against these evil geniuses more than once. And on one occasion, against several duplicates of themselves. Thankfully, their heroic opposite numbers still proved superior!
Doctor Thaddeus Bogus Sivana was once an aspiring physicist who invented various revolutionary devices for the benefit of mankind. And yet, secular authorities scoffed at him, and as a result Sivana swore revenge against his fellow man. From that point forward, upon meeting the World's Mightiest Mortal, Sivana was Captain Marvel's most persistent and deadly foe. In fact, on on occasion he trapped the hero and his allies in suspendium. Alas, the mad mental menace and his family was also captured and held in stasis along with the heroic Marvels in suspended animation for decades. Even after his revival, Sivana never won except once when his inventions were actually acclaimed to the point where he received a Nobel Peace Prize when Marvel used them to aid mankind... much to Sivana's chagrine!
Doctor Spectro also wanted to use his colored light technology for the medical benefits of mankind. However, once he was attacked by a gang of opportunistic hoods and his beam was reflected back on himself, Spectro turned evil and gained vast powers which he used against Captain Atom on more than one occasion... including when a miniature malicious mob of his clones attached the Atomic Avenger intent on reassembling Spectro into one man once more. Yet a good persona existed in the group of Docs, who attempted to exert control over the reconstituted Spectro later.
An analog for Sivana over at MLJ/Mighty Comics would probably be the Fly's arch-foe the Spider, another deformed bald midget of malice with a mind for marvelous machinery.
In 1954, aspiring comic book publisher Charlton purchased the rights to several prominent characters from the expiring Fawcett Comics, such as Ibis, Golden Arrow and Lance O'Casey. In 1980 and 1985, DC Comics purchase Fawcett's Marvel Family then Charlton's Action Heroes, and the two were linked once more, now on parallel Earths, Four and Shazam.Now the MLJ has been added to their stable of characters, we examine the parallels in this series.