From what we could tell while visiting the set, it will be Mordo (Chiwetel Ejiofor) who recruits Strange, but Wong who helps to properly train him.
The focus of this new trailer falls on Stephen Strange, renowned neurosurgeon, encountering The Ancient One, the one-time manservant of Doctor Strange — in the comics, at least — who has now become a trained warrior in the Ancient One’s Karma-Taj who ends up collaborating with Strange, though more as a peer.