The Gemara (especially the Bavli, not so much the Yerushalmi) is replete with countless references to demons. Nevertheless, Rambam (as well as others such as Ralbag, R. Yaakov b. Abba Mari Anatoli, R. Levi ben Avraham ben Chaim, and probably Meiri and Ibn Ezra) were of the view that there is no such thing. Rambam does not explicitly deny the existence of demons, but it clearly emerges from many different discussions of his.
It is not only contemporary academic scholars who realize that Rambam did not believe in demons. As Marc Shapiro documents in his fascinating Studies in Maimonides and his Interpreters, there were many traditional Torah scholars who also realized this, including R. Shlomo b. Meshullam da Piera, R. Yosef b. Shem Tov, R. Yosef Shlomo Delmedigo, R. Aviad Sar-Shalom Basilea, Abarbanel, the Vilna Gaon, R. Yosef Ergas, R. Yosef Shaul Nathanson, R. Menashe ben Yisrael, R. Eliezer Simchah Rabinowitz, and R. Yosef Kapach. Some of these agreed with Rambam, others criticized him for this denial.
But many traditionalists simply could not imagine that the great Rambam could deny the existence of something that played so prominent a role in Chazal's worldview and even in halachah. Shapiro cites a long list of authorities who claimed that Rambam really did believe in demons. Even someone as relatively broad-minded as R. Yaakov Kaminetzky z"l wrote that when Rambam wrote that magic and the occult is all nonsense, he was only speaking about the magic practiced in his day, and was not referring to that of the Biblical and Talmudic era. He claims that Rambam agreed with Ramban that magic, demons and so on did actually exist.
This sort of historical revisionism is well known amongst traditionalists. But I discovered a fascinating new example of it amongst people who, one might expect, would be very different. Here we find someone claiming that Chazal themselves did not believe in demons (as actual entities), and here he claims that Ramban and all the other Rishonim did not believe in them either.
This is not only untenable, but absurd. Along with virtually the entire ancient world, Ramban certainly believed in demons, and writes at length about them. He describes them as being produced by witchcraft and possessing bodies composed of air that cannot be detected, along with the element of fire. Since they are composed of these light elements, they are able to fly, and since they travel in the sky, they are able to learn about future events from the angels of the constellations. Ramban also explains Chazal’s statement about demons eating like people to mean that they also subsist on food – although theirs consists of evaporated moisture and smoke from fires. He also views the denial of the existence of demons as signifying a general heretical worldview, berating Aristotle for denying the existence of that which cannot be empirically detected. It is quite clear that Ramban believed in the existence of actual demons, as did Chazal.
I'm not sure how to categorize this latter kind of revisionism, which seeks to read the Rambam's rationalism into all other great Torah authorities. Should it be termed hyper-rationalist? Fundamentalist-rationalist? Irrational rationalist? It's difficult to find a label that is accurately descriptive without being offensive.