There was also a tendency to draw villains as the devil, with the saturnine features, and even horns on their helmets like Magneto, Mandarin, and Loki.
Those who weren't drawn as the devil were often drawn as some other image of evil. The Mandarin was often drawn with acromegalic features, suggesting brutishness.
He's essentially an Uruk-Hai with the jewelry of an exploiting aristocrat or exploiting pimp.
Doctor Doom is, of course, an image of the grim reaper.
Kingpin is an ogre.
And so on. If you look at most supervillains, they are images of the devil, or savagery, or death, or grotesque wealth. Or even a combination.