Mimio

The Mysterious Underground Men begins with an "opening credits" giving biographies of major and minor characters. While the biographies don't tell the entire story, they spoil the major twists and the ending. Notably, though, Mimio is absent, even though they are present throughout the story and  instrumental in the defeat of the termites. Meanwhile the termites get their own collective mention (even if the Queen's plot mostly involves bribing humans to fight for her), as well as the three workers (only one of whom is named in story).

While leaving out Mimio from the listed cast (and the cover) preserves some element of suspense, Mimio was a more important and interesting character than Young John. Although in the place of the talking animal sidekick, Mimio really drives the plot forward. Young John's biography gives him full credit for defeating the termites, but he would not have been able to do so without Mimio helping him at multiple stages (especially at the end, when Mimio single-handedly retrieves the blueprints and fossil diamond and kills the Queen). While on the surface being about Young John's adventure, The Mysterious Underground Men is really more about Mimio and their quest to be human.