Complex sentence: He has most often been the central villain of the X-Men comics, as well as the TV shows and the films, although in the comics he has been an ally and even member of the X-Men at times.
Split into simpler sentences: He has most often been the primary villain of the X-Men comics, as well as the TV shows and the films. Although in the comics, he has been an ally and even member of the X-Men at times.