To learn who rules over you, simply find out who you are not allowed to criticize.

Voltaire (1694-1778) French writer [pseud. of Francois-Marie Arouet]

(Misattributed)

Frequently attributed to Voltaire in memes, but unsourced in any of his writings. More accurately attributed to Kevin Alfred Strom during a 1993 anti-semitic screed on a radio broadcast:

To determine the true rulers of any society, all you must do is ask yourself this question: Who is it that I am not permitted to criticize?

More discussion of the attribution here, here and here.