(Adventure Comics 046, 1940)
The Coin is a few different super-villain clichés rolled into one. Firstly he’s an old college chum of Wesley “Sandman” Dodds, and “old schoolmate of hero turns out to be villain” is as much a recurring thing in comics as an old friend showing up and immediately dying. Which the Coin also does.
Finally, the Coin is a man who dresses up as an old lady to do crime, which is a super-villain bit and also something that regular-style crooks are apt to do in the Golden and Silver Ages. Old women are such unlikely villains that everyone else poses as them – even Catwoman, in her first appearance.
Anyway, he’s a counterfeiter.