Dictator

(n) a ruler who is unconstrained by law

From The Boston Globe:

WASHINGTON — President Bush has quietly claimed the authority to disobey more than 750 laws enacted since he took office, asserting that he has the power to set aside any statute passed by Congress when it conflicts with his interpretation of the Constitution.

Here’s a comparison to other presidents and some examples.

Thanks to Dan Froomkin of The Washington Post for pointing this out.

UPDATE: Some more commentary from Slate.