Balek is the god of the Empire, with the Emperor the body he chooses to dwell in. He along is allowed to wield magic in the Empire and he has killed any other who shows the ability.
Balek is eternal, transferring his spirit and favor from Emperor to Emperor. If another believes that Balek has abandon the Emperor then they may challenge the Emperor. The challenge takes the form of a battle by magics. Whoever has the spirit of Balek dwelling within them will be victorious, and Balek slaughters the pretender.