Pluto, you are still a planet in my heart Mug

When you think about the obsession in speculative fiction with the idea of a hidden planet, a malevolent influence hosting everything evil and nefarious in the galaxy waiting in the dark to strike on an unsuspecting galaxy, that's Pluto. It's not his fault: it all started when Le Verrier predicted the existence of an undiscovered planet based on the available data. The idea of a dark planet that none can see but that can disturb the actions of other solar objects was so evocative that it quickly appeared in literature and art, for instance as Yuggoth in the Cthulhu cycle from H.P. Lovecraft. At some point Pluto was called "Planet X": is there anything more vintage science fiction that a planet named Planet X? You can theremin music.