Generally, when we think of fandoms, they’re centered around a broad property like Star Wars or Harry Potter. They can become popular because people become enamored with the world that’s been created, and they can see themselves inhabiting it. Whether that’s riding shotgun aboard the Millennium Falcon, or donning the Stromtrooper armor and purging Jedi from the galaxy, or simply being a bartender on Coruscant, they can see themselves in that world dealing with the same types of people and situations the characters are dealing with. And while they can and frequently do pay respects to the initial creator(s) behind it, they fall in love with the ideas in the stories more than anything else.
L. Frank Baum famously wrote The Wonderful Wizard of Oz in 1900. It was wildly popular, and it was adapted into a Broadway musical before Baum could complete his first sequel. The famous 1939 movie starring Judy Garland? That was actually the fourth time the book had been translated to film! Readers clearly loved the Oz stories, and every one that Baum wrote sold well. But even after Baum died in 1919, his publisher continued putting more Oz books out, calling in creators like Ruth Plumly Thompson and John R. Neill, who illustrated many of Baum’s books. The stories remained so amazingly popular that they wound up publishing nearly twice as many more than Baum himself wrote!
But less talked about are the fandoms of creators. People who follow the works of an individual and are more enamored by their thoughts and ideas than the express form in which they’re realized. You would sometimes see hints of this in certain creators who’s works were all of high caliber. Someone like movie director Alfred Hitchcock or science fiction author Isaac Asimov. Their works are poured over and studied, with others often trying to learn for creators who have a high degree of mastery of their craft. But in most cases, the study of the creator focuses on their use of a specific medium, and how they were able to achieve that perceived mastery.
More recently, though, we’re seeing audiences starting to look at and follow creators for their ideas, regardless of medium. Someone like Neil Gaiman, for example, who made his name for himself writing comics, has gone on to work on radio, prose and film, not just by adapting his previous works but by creating new stories expressly for those media. He’s developed a fanbase that follow his works, regardless of whether he’s writing Sandman comics the Neverwhere television show. That the worlds remain distinct and separate is immaterial; fans are more interested in seeing what ideas Gaiman is able to present.
These types of fans, I think, express themselves differently in some respects. Wearing a Spider-Man costume could be in reference to any number of works created by any number of creators, but trying to embody the breadth of a creator’s output can be more challenging. (Although I have seen someone try to cosplay as every character Johnny Depp character simultaneously, so it’s not unheard of!) But at the end of the day, it still boils down to people trying to connect with one another via images and ideas, whether they’re embodied in the body of work surrounding a central theme, or the body of work from a single individual.