Mermen And Martians

Here is a really obscure fannish parallel between Poul Anderson and Neil Gaiman that no one else would have thought of:

Anderson's works include mermen, in The Merman's Children, and several races of Martians;

Gaiman's Morpheus, Lord of Dreams, the title character of The Sandman, coexists with the DC Comics superheroes who include not only the famous Kryptonian, masked avenger and Amazon but also an amphibious Atlantean (also here) and a last surviving Martian who sees Morpheus as an appropriate deity of his planet.

These are very different scenarios with some archetypal parallels.