The Ancient One is Doctor Strange's mentor, the previous Sorcerer Supreme, and also the man who trained the film's rumored villain, Baron Mordo.
If a deal gets done, The Grand Budapest Hotel and Moonrise Kingdom actress will be mentoring Benedict Cumberbatch (Sherlock). It will also mean that the Tibetan mystic will be going through a gender swap as the Ancient One is a male character in the comics
Doctor Strange is scheduled to begin filming this November and will be directed by Scott Derrickson. The film will open in theaters November 4, 2016.