Answer:

dualist

Answer	Crossword Clue
DUALIST	Believer in a pair of opposed eternal principles
DUALIST	Adherent of a twofold system.
DUALIST	Advocate of a twofold doctrine

DUALIST	Believer in a world of good vs. evil
DUALIST	One who believes there are two eternal principles, one good and one evil
DUALIST	Believer in a binary system