Which X men professor appears in the comics series X-Men?

There have been a few different people who have taken on the mantle of Professor X in the X-Men comics, but the most prominent and well-known is Charles Xavier.

While there have been others like Charles Xavier Jr. (Legion), Moira MacTaggert, and even Magneto who have briefly held the role, Charles Xavier is the definitive Professor X and the one most closely associated with the X-Men.