X-ian

X-ian was a term used by Americans who identified as fans of the British science fiction television series Professor X. This came to the horror of older British fans who adhered to the "politely-named" Professor X Appreciation Association. Rezaul Kapoor also identified as an X-ian. (PROSE: Escape Velocity)

Behind the scenes
With Professor X serving as equivalent to Doctor Who within the Doctor Who universe, X-ian is a clear analogue to the term Whovian.