Kaecilius

Played by Mads Mikkelsen

Kaecilius is a former student of the Ancient One who grew disillusioned with Kamar-Taj's teachings after losing his family, turning instead to the Dark Dimension and its ruler, Dormammu, in pursuit of immortality outside the flow of time. Leading a group of zealot sorcerers, he attempted to bring Earth into the Dark Dimension before being stopped by Doctor Strange.

First turns up in Doctor Strange.