The Ancient One teaches both Stephen Strange and villain Baron Mordo the ways of mystical arts. A leading role that allows for some diverse casting which makes both Watanabe and Freeman a preference. While Freeman's voice could be amazing for the role, I'd prefer to see Watanabe. It's not shocking that Ken is in the mix, as the training scenes in Batman Begins sort of parallels the origin of Doctor Strange.
Daniel Bruhl's (Inglorious Basterds, Rush) role in Captain America: Civil War is said to crossover to Strange as well. This has us believing he could be playing Karl Mordo, or combination with Captain America villain Baron Zemo.