In the comics, Mordo and Doctor Strange are both pupils of the Tibetan sorcerer known as The Ancient One. Strange thwarts Mordo’s plot to kill his teacher, and in return is trained by The Ancient One in the art of magic in order to be a formidable opponent to the villainous Mordo.
However, Deadline reports that the film’s iteration of Mordo might be quite different. In keeping with the gender twisting casting of Tilda Swinton for The Ancient One (how brilliant is that choice?), the report notes that the movie version of Mordo is “an amalgamation of characters culled from Doctor Strange’s mythology” and cautions that he won’t necessarily be a completely villainous character.