A defining thread of modern scientific thought is skepticism, the tendency to question accepted ideas until evidence is found to confirm or reject them. But what do skeptics do in worlds of magic, aliens, and other matters fantastic?
Science fiction authors often face a difficult task in incorporating skepticism into their works. After all, they're usually science fiction authors for a reason, and they want to incorporate a key part of the scientific mindset into their works. But what are you supposed to do when that mindset would just make any character who possesses it spend the entire story repeatedly pointing out that the entire story is impossible? There are two options - either you modify the boundaries of the character's skepticism to incorporate whatever impossible science works in this universe...or you just sort of drop a rational skeptic from our world into this science fiction landscape more or less unaltered. And that's where things tend to get a bit weird.
Because it's me, I've got to crowbar an Isaac Asimov reference in somehow. In this case, the Good Doctor actually makes things fairly easy, since he introduces a character in Foundation and Earth who actually calls himself a Skeptic, with the capital "S" and everything. This man, the wonderfully named Vasil Deniador, provides a fairly workable definition for what being a skeptic might mean in a universe of interstellar travel and a dead man's equations directing the course of history, along with why skeptics aren't particularly well-liked: