Kaecilius

Portrayed by Mads Mikkelsen, Kaecilius is the main antagonist of the movie. In the comics, he is also an errand boy and a disciple of Baron Mordo. We still don’t know whether this connection has been kept in the movie, as well.

According to the character’s description, he is also a very powerful sorcerer – and I guess everybody has seen his awesome magical powers in the trailers. He used to be one of the good guys, until he stumbled upon something from another dimension, something that seduced him.

So he finds something better and wants to change the world according to this new vision. This falls in line with quite a few other villains of the MCU, who don’t desire power for the sake of power. Kingpin and Alexander Pierce are the best examples.

Of course, there is also another possibility, one that might turn out to be true. Especially if some of the accidental reveals concerning the movie turn out to be true and not some sort of misdirection.