In Other Media
Kaecillius is the main antagonist of the film, portrayed by Danish actor Mads Mikkelsen. He is a much more significant character here, and has a characterization more in line with Baron Mordo, his master from the comics.
Here, Kaecilius is a former disciple of the Ancient One who betrayed her and went rogue. He now serves Dormammu, and seeks to bring his master and the Dark Dimension to Earth in order to gain everlasting life. However, Strange manages to thwart Dormammu, resulting in Kaecilius and his followers becoming trapped in the Dark Dimension, where they are forced to live an agony and torment for all of eternity.